Remove unnecessary bottom margin for TabView on mac

This extra padding at the bottom is not needed and only serves to
make the borders uneven on mac.

Change-Id: Ibb3f8a3ba1f37ce1e9c6674a53cfb13e257fb97f
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>

src/controls/TabView.qml

@@ -198,7 +198,7 @@ FocusScope {
             anchors.fill: parent
             anchors.margins: (frameVisible ? frameWidth : 0)
             anchors.topMargin: anchors.margins + (style =="mac" ? 6 : 0)
-            anchors.bottomMargin: anchors.margins + (style =="mac" ? 6 : 0)
+            anchors.bottomMargin: anchors.margins
 
             property int frameWidth
             property string style