ReleaseNotes: fix typo reported by Eugene

git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_38@260984 91177308-0d34-0410-b5e6-96231b3b80d8

docs/ReleaseNotes.rst

@@ -228,7 +228,7 @@ Several new checks were added:
   ``-enable-checker optin.performance.Padding``.
 - The checks to detect misuse of ``_Nonnull`` type qualifiers as well as checks
   to detect misuse of Objective-C generics were added.
-- The analyzer now has opt in checks to detect localization errors in Coca
+- The analyzer now has opt in checks to detect localization errors in Cocoa
   applications. The checks warn about uses of non-localized ``NSStrings``
   passed to UI methods expecting localized strings and on ``NSLocalizedString``
   macros that are missing the comment argument. These can be enabled by passing