Add changelog entry for 3.2.1-solc-0.7

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 3.2.1-solc-0.7 (unreleased)
+
+* `ERC777`: Remove a warning about function state visibility in Solidity 0.7. ([#2327](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2327))
+
 ## 3.2.0 (2020-09-10)
 
 ### New features