Update Contracts docs to make examples compile (#2170)

* Update access-control.adoc to make compile

Add call to `ERC20("MyToken", "TKN")` in `MyToken` constructor

* Update access-control.adoc to make compile

Add call to `ERC20("MyToken", "TKN")` in `MyToken` constructor

* Update access-control.adoc MyToken formatting

* Update erc20-supply.adoc to make compile

Add call to `ERC20("MyToken", "TKN")` in `ERC20FixedSupply` constructor

* Update erc20-supply.adoc to make compile

Add constructor to `ERC20WithMinerReward`

* Update erc20-supply.adoc to make compile

In `MinerRewardMinter` use `ERC20MinterPauser`

* Update erc20-supply.adoc to make compile

Add constructor and override to `ERC20WithAutoMinerReward`

* Update erc777.adoc to make compile

* Update gsn-strategies.adoc to make compile

* Update gsn-strategies.adoc to make compile

Fix imports, add overrides, and revert reason to `MyContract`

docs/modules/ROOT/pages/access-control.adoc

@@ -67,7 +67,7 @@ contract MyToken is ERC20, AccessControl {
     // Create a new role identifier for the minter role
     bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
 
-    constructor(address minter) public {
+    constructor(address minter) public ERC20("MyToken", "TKN") {
         // Grant the minter role to a specified account
         _setupRole(MINTER_ROLE, minter);
     }
@@ -97,7 +97,7 @@ contract MyToken is ERC20, AccessControl {
     bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
     bytes32 public constant BURNER_ROLE = keccak256("BURNER_ROLE");
 
-    constructor(address minter, address burner) public {
+    constructor(address minter, address burner) public ERC20("MyToken", "TKN") {
         _setupRole(MINTER_ROLE, minter);
         _setupRole(BURNER_ROLE, burner);
     }
@@ -140,7 +140,7 @@ contract MyToken is ERC20, AccessControl {
     bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
     bytes32 public constant BURNER_ROLE = keccak256("BURNER_ROLE");
 
-    constructor() ERC20("MyToken", "TKN") public {
+    constructor() public ERC20("MyToken", "TKN") {
         // Grant the contract deployer the default admin role: it will be able
         // to grant and revoke any roles
         _setupRole(DEFAULT_ADMIN_ROLE, msg.sender);

docs/modules/ROOT/pages/erc20-supply.adoc

@@ -26,7 +26,7 @@ Starting with Contracts v2 this pattern is not only discouraged, but disallowed.
 [source,solidity]
 ----
 contract ERC20FixedSupply is ERC20 {
-    constructor() public {
+    constructor() public ERC20("Fixed", "FIX") {
         _mint(msg.sender, 1000);
     }
 }
@@ -44,6 +44,8 @@ The mechanism we will implement is a token reward for the miners that produce Et
 [source,solidity]
 ----
 contract ERC20WithMinerReward is ERC20 {
+    constructor() public ERC20("Reward", "RWD") {}
+
     function mintMinerReward() public {
         _mint(block.coinbase, 1000);
     }
@@ -64,9 +66,9 @@ The accounts with the minter role don't need to be externally owned, though, and
 [source,solidity]
 ----
 contract MinerRewardMinter {
-    ERC20DeployReady _token;
+    ERC20MinterPauser _token;
 
-    constructor(ERC20DeployReady token) public {
+    constructor(ERC20MinterPauser token) public {
         _token = token;
     }
 
@@ -90,11 +92,13 @@ Adding to our previous supply mechanism, we can use this to mint a miner reward
 [source,solidity]
 ----
 contract ERC20WithAutoMinerReward is ERC20 {
+    constructor() public ERC20("Reward", "RWD") {}
+
     function _mintMinerReward() internal {
         _mint(block.coinbase, 1000);
     }
 
-    function _transfer(address from, address to, uint256 value) internal {
+    function _transfer(address from, address to, uint256 value) internal override {
         _mintMinerReward();
         super._transfer(from, to, value);
     }

docs/modules/ROOT/pages/erc777.adoc

@@ -18,7 +18,7 @@ We will replicate the `GLD` example of the xref:erc20.adoc#constructing-an-erc20
 
 [source,solidity]
 ----
-pragma solidity ^0.5.0;
+pragma solidity ^0.6.0;
 
 import "@openzeppelin/contracts/token/ERC777/ERC777.sol";
 
@@ -30,7 +30,7 @@ contract GLDToken is ERC777 {
         ERC777("Gold", "GLD", defaultOperators)
         public
     {
-        _mint(msg.sender, msg.sender, initialSupply, "", "");
+        _mint(msg.sender, initialSupply, "", "");
     }
 }
 ----

docs/modules/ROOT/pages/gsn-strategies.adoc

@@ -59,7 +59,7 @@ Instead of using `GSNRecipient` directly, your GSN recipient contract will inste
 
 [source,solidity]
 ----
-import "@openzeppelin/contracts/GSN/GSNRecipientSignature";
+import "@openzeppelin/contracts/GSN/GSNRecipientSignature.sol";
 
 contract MyContract is GSNRecipientSignature {
     constructor(address trustedSigner) public GSNRecipientSignature(trustedSigner) {
@@ -106,8 +106,8 @@ Your GSN recipient contract needs to inherit from `GSNRecipientERC20Fee` along w
 
 [source,solidity]
 ----
-import "@openzeppelin/contracts/GSN/GSNRecipientERC20Fee";
-import "@openzeppelin/contracts/access/AccessControl";
+import "@openzeppelin/contracts/GSN/GSNRecipientERC20Fee.sol";
+import "@openzeppelin/contracts/access/AccessControl.sol";
 
 contract MyContract is GSNRecipientERC20Fee, AccessControl {
     bytes32 public constant MINTER_ROLE = keccak256("MINTER_ROLE");
@@ -116,8 +116,16 @@ contract MyContract is GSNRecipientERC20Fee, AccessControl {
         _setupRole(MINTER_ROLE, _msgSender());
     }
 
+    function _msgSender() internal view override(Context, GSNRecipient) returns (address payable) {
+        return GSNRecipient._msgSender();
+    }
+
+    function _msgData() internal view override(Context, GSNRecipient) returns (bytes memory) {
+        return GSNRecipient._msgData();
+    }
+
     function mint(address account, uint256 amount) public {
-        require(hasRole(MINTER_ROLE, _msgSender()));
+        require(hasRole(MINTER_ROLE, _msgSender()), "Caller is not a minter");
         _mint(account, amount);
     }
 }