shadow not appearing

[rchincho]

somehow iam not getting shadow on fab buttom.

using appcompact support library.

<com.melnykov.fab.FloatingActionButton
android:id="@+id/fabIcon"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/ic_add_white_24dp"
app:fab_colorNormal="@color/accent"
app:fab_colorPressed="@color/accent_dark"
app:fab_shadow="true"
android:layout_alignParentBottom="true"
android:layout_alignParentRight="true"
android:layout_marginBottom="@dimen/activity_horizontal_margin"
android:layout_marginRight="@dimen/activity_horizontal_margin"/>