Merge pull request #421 from firebase/bugfix/sdkversion

Downgraded minSdkVersion to 14

Author: Alex Ames

messaging/src/android/java/LibraryManifest.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="com.google.android.gms.messaging.cpp" >
-    <uses-sdk android:minSdkVersion='26'/>
+    <uses-sdk android:minSdkVersion='14'/>
     <application>
         <service
             android:name="MessageForwardingService"