Use a CocoaPods-specific tag (#5711)

Author: paulb777

Firebase.podspec

@@ -13,7 +13,7 @@ Simplify your app development, grow your user base, and monetize more effectivel
 
   s.source           = {
     :git => 'https://github.com/firebase/firebase-ios-sdk.git',
-    :tag => s.version.to_s
+    :tag => 'CocoaPods-' + s.version.to_s
   }
 
   s.preserve_paths = [

Releases/update-versions.py

@@ -171,7 +171,7 @@ def GenerateTag(pod, version):
     Tag.
   """
   if pod == "Firebase":
-    return version
+    return 'CocoaPods-{}'.version
   if pod.startswith("Firebase"):
     return '{}-{}'.format(pod[len('Firebase'):], version)
   if pod.startswith("Google"):