Update CHANGELOG for 7.2.0 release (#436)

Author: mdmathias

CHANGELOG.md

@@ -1,3 +1,11 @@
+# 7.2.0
+- General release adding Firebase App Check support to establish your
+application's integrity while signing in with Google
+- Internal
+  - Add instancetype return to test helper ([#393](https://github.com/google/GoogleSignIn-iOS/pull/393))
+  - Remove GTMSessionFetcher modular import ([#403](https://github.com/google/GoogleSignIn-iOS/pull/403))
+  - Bump activesupport from 5.2.5 to 5.2.8.1 in the bundler group ([#429](https://github.com/google/GoogleSignIn-iOS/pull/429))
+
 # 7.1.0-fac-beta-1.1.0
 - Beta release supporting Firebase App Check tokens used
 to establish your application's integrity while signing in with Google