Fixup comments

Author: blaugold

packages/google_sign_in/google_sign_in/lib/google_sign_in.dart

@@ -232,8 +232,8 @@ class GoogleSignIn {
 
   /// Client ID being used to connect to google sign-in.
   ///
-  /// This option is not supported on all platforms (e.g., Android). It is
-  /// optional, if file-based configuration is used.
+  /// This option is not supported on all platforms (e.g. Android). It is
+  /// optional if file-based configuration is used.
   ///
   /// The value specified here has precedence over a value from a configuration
   /// file.
@@ -242,8 +242,8 @@ class GoogleSignIn {
   /// Client ID of the backend server to which the app needs to authenticate
   /// itself.
   ///
-  /// Optional and not supported on all platforms (e.g., web). Per default, it
-  /// is initialized from a configuration file, if available.
+  /// Optional and not supported on all platforms (e.g. web). By default, it
+  /// is initialized from a configuration file if available.
   ///
   /// The value specified here has precedence over a value from a configuration
   /// file.