Don't need a viewbox here

Author: shana

src/GitHub.VisualStudio/Resources/icons/mark_github.xaml

@@ -1,18 +1,13 @@
-<Viewbox
-    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
-    xmlns:cache="clr-namespace:GitHub.VisualStudio.Helpers"
-    xmlns:ui="clr-namespace:GitHub.UI;assembly=GitHub.UI"
-  >
-  <Viewbox.Resources>
+<ui:OcticonImage xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+                 xmlns:cache="clr-namespace:GitHub.VisualStudio.Helpers"
+                 xmlns:ui="clr-namespace:GitHub.UI;assembly=GitHub.UI"
+                 Foreground="{DynamicResource VsBrush.ToolWindowText}"
+                 Icon="mark_github">
+  <ui:OcticonImage.Resources>
     <ResourceDictionary>
       <ResourceDictionary.MergedDictionaries>
         <cache:SharedDictionaryManager Source="pack://application:,,,/GitHub.UI;component/SharedDictionary.xaml" />
       </ResourceDictionary.MergedDictionaries>
     </ResourceDictionary>
-  </Viewbox.Resources>
-    <ui:OcticonImage 
-        Icon="mark_github"
-        VerticalAlignment="Center"
-        Background="{DynamicResource VsBrush.ToolWindowText}"
-        />
-</Viewbox>
+  </ui:OcticonImage.Resources>
+</ui:OcticonImage>