Add INTERNET and ACCESS_NETWORK_STATE to database permissions.
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.google.firebase.database">
<uses-sdk android:minSdkVersion="14"/>
+
+ <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+ <uses-permission android:name="android.permission.INTERNET" />
</manifest>
