removed invalid example from import github file (#928)

apps/remix-ide/src/app/ui/landing-page/landing-page.js

@@ -406,7 +406,7 @@ export class LandingPage extends ViewPlugin {
                       <p class="mt-3 mb-0"><label>IMPORT FROM:</label></p>
                       <div class="btn-group">
                         <button class="btn mr-1 btn-secondary" data-id="landingPageImportFromGistButton" onclick="${() => importFromGist()}">Gist</button>
-                        <button class="btn mx-1 btn-secondary" onclick="${() => load('Github', 'github URL', ['https://github.com/0xcert/ethereum-erc721/src/contracts/tokens/nf-token-metadata.sol', 'https://github.com/OpenZeppelin/openzeppelin-solidity/blob/67bca857eedf99bf44a4b6a0fc5b5ed553135316/contracts/access/Roles.sol', 'github:OpenZeppelin/openzeppelin-solidity/contracts/ownership/Ownable.sol#v2.1.2'])}">GitHub</button>
+                        <button class="btn mx-1 btn-secondary" onclick="${() => load('Github', 'github URL', ['https://github.com/0xcert/ethereum-erc721/src/contracts/tokens/nf-token-metadata.sol', 'https://github.com/OpenZeppelin/openzeppelin-solidity/blob/67bca857eedf99bf44a4b6a0fc5b5ed553135316/contracts/access/Roles.sol'])}">GitHub</button>
                         <button class="btn mx-1 btn-secondary" onclick="${() => load('Swarm', 'bzz-raw URL', ['bzz-raw://<swarm-hash>'])}">Swarm</button>
                         <button class="btn mx-1 btn-secondary" onclick="${() => load('Ipfs', 'ipfs URL', ['ipfs://<ipfs-hash>'])}">Ipfs</button>
                         <button class="btn mx-1 btn-secondary" onclick="${() => load('Https', 'http/https raw content', ['https://raw.githubusercontent.com/OpenZeppelin/openzeppelin-contracts/master/contracts/token/ERC20/ERC20.sol'])}">https</button>