Fix warning exposed by Xcode 12 (#5876)

FirebaseMessaging/CHANGELOG.md

@@ -1,3 +1,6 @@
+# 2020-06 -- Unreleased
+- [fixed] Fix documentation warning exposed by Xcode 12. (#5876)
+
 # 2020-06 -- v4.5.0
 - [changed] Use UNNotificationRequest to schedule local notification for local timezone notification for iOS 10 and above. This should also fix the issue that '%' was not properly shown in title and body. (#5667)
 - [fixed] Fixed Maltese language key for language targeting. (#5702)

FirebaseMessaging/Sources/FIRMessagingPubSub.m

@@ -280,7 +280,7 @@ static NSString *const kTopicRegexPattern = @"/topics/([a-zA-Z0-9-_.~%]+)";
 /**
  *  Gets the class describing occurences of topic names and sender IDs in the sender.
  *
- *  @param expression The topic expression used to generate a pubsub topic
+ *  @param topic The topic expression used to generate a pubsub topic
  *
  *  @return Representation of captured subexpressions in topic regular expression
  */