[android] show menu icon always

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" > <-- added this line

  <item
    android:id="@+id/action_settings"
    android:icon="@android:drawable/ic_menu_add"
    android:title="@string/action_settings"
    app:showAsAction="always"/> <-- added this line. not android:showAsAction

</menu>

도움받은 곳 : http://stackoverflow.com/a/18380187/1025379