Merging the 6.3.0 release into master (#3217)

* Update versions for Release 6.3.0

* Revert "Raise exception when log into Facebook using OAuth.  (#3138)" (#3208) (#3209)

This reverts commit 393d060710.

FirebaseAuth.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'FirebaseAuth'
-  s.version          = '6.1.1'
+  s.version          = '6.1.2'
   s.summary          = 'The official iOS client for Firebase Authentication (plus community support for macOS and tvOS)'
 
   s.description      = <<-DESC