Update CODEOWNERS: Wallet Framework -> Core Platform (#405)

Author: mcmire

.github/CODEOWNERS

@@ -1,6 +1,6 @@
 # Lines starting with '#' are comments.
 # Each line is a file pattern followed by one or more owners.
 
-*                                   @MetaMask/wallet-framework-engineers
+*                                   @MetaMask/core-platform
 src/methods                         @MetaMask/wallet-api-platform-engineers @MetaMask/confirmations
 src/wallet.*                        @MetaMask/wallet-api-platform-engineers @MetaMask/confirmations