I got the following Error in android Studio 2.2.3 when I sync gradle.
Error:Cause: unable to find valid certification path to requested target
You are using older version of libraries.
compile 'com.android.support:appcompat-v7:25.2.0' compile 'com.android.support:design:25.2.0' compile 'com.android.support:palette-v7:25.2.0' compile 'com.google.firebase:firebase-messaging:10.2.0'