move changelog entry to new features section

(cherry picked from commit 2d30415373)

CHANGELOG.md

@@ -9,10 +9,11 @@
  * Added replacement for functions that don't forward all gas (which have been deprecated): ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))
    * `PullPayment.withdrawPaymentsWithGas(address payable payee)`
    * `Escrow.withdrawWithGas(address payable payee)`
+ * `SafeMath`: added support for custom error messages to `sub`, `div` and `mod` functions. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
 
 ### Improvements:
  * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))
- * `SafeMath`: added custom error messages support for `sub`, `div` and `mod` functions. `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
+ * `ERC20` and `ERC777` updated to throw custom errors on subtraction overflows. ([#1828](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1828))
 
 ### Deprecations:
  * Deprecated functions that don't forward all gas: ([#1976](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1976))