Update CHANGELOG to prepare for 9.1.0 release

Author: AkshatG6

CHANGELOG.md

@@ -1,6 +1,5 @@
 # 9.1.0
 - Allow requesting `claims` (currently, only `auth_time`) via [Sign-in methods](https://github.com/google/GoogleSignIn-iOS/blob/gandhiakshat/update-changelog-for-9.1.0-release/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h#L240) ([#550](https://github.com/google/GoogleSignIn-iOS/pull/550), [#552](https://github.com/google/GoogleSignIn-iOS/pull/552), [#553](https://github.com/google/GoogleSignIn-iOS/pull/553), [#569](https://github.com/google/GoogleSignIn-iOS/pull/569))
-- Allow requesting `claims` (currently, only `auth_time`) via [Sign-in methods](https://github.com/google/GoogleSignIn-iOS/blob/gandhiakshat/update-changelog-for-9.1.0-release/GoogleSignIn/Sources/Public/GoogleSignIn/GIDSignIn.h#L240) ([#550](https://github.com/google/GoogleSignIn-iOS/pull/550), [#552](https://github.com/google/GoogleSignIn-iOS/pull/552), [#553](https://github.com/google/GoogleSignIn-iOS/pull/553), [#569](https://github.com/google/GoogleSignIn-iOS/pull/569))
 - Update `addScopes:` methods in `GIDSignIn` to include previously requested `claims` ([#557](https://github.com/google/GoogleSignIn-iOS/pull/557))
 - Internal
   - Assign to `keychainStore` asap in initializer ([#540](https://github.com/google/GoogleSignIn-iOS/pull/540))