Fix bug in MetroAnimatedSingleRowTabControl when tabs not on top

This should work with TabStripPlacement="Left", for example this way:

       <mahappsmc:MetroAnimatedSingleRowTabControl TabStripPlacement="Left">  
            <TabControl.Resources>
                <Style TargetType="{x:Type TabItem}" BasedOn="{StaticResource {x:Type TabItem}}">
                    <Setter Property="HeaderTemplate">
                        <Setter.Value>
                            <DataTemplate>
                                <ContentPresenter Content="{TemplateBinding Content}">
                                    <ContentPresenter.LayoutTransform>
                                        <RotateTransform Angle="270" />
                                    </ContentPresenter.LayoutTransform>
                                </ContentPresenter>
                            </DataTemplate>
                        </Setter.Value>
                    </Setter>
                </Style>
            </TabControl.Resources>
            <TabItem Header="Test">
            Test   
            </TabItem>
        </mahappsmc:MetroAnimatedSingleRowTabControl>