Add dependency on Team Explorer extension

Author: jcansdale

src/GitHub.VisualStudio/source.extension.vsixmanifest

@@ -18,6 +18,7 @@
   <Dependencies>
     <Dependency Id="Microsoft.Framework.NDP" DisplayName="Microsoft .NET Framework" d:Source="Manual" Version="[4.5,)" />
     <Dependency Id="Microsoft.VisualStudio.MPF.14.0" DisplayName="Visual Studio MPF 14.0" d:Source="Installed" Version="[14.0,]" />
+    <Dependency Id="Microsoft.VisualStudio.TeamFoundation.TeamExplorer.Extensions" DisplayName="Team Explorer" d:Source="Installed" Version="[14.0,16.0)" />
   </Dependencies>
   <Assets>
     <Asset Type="Microsoft.VisualStudio.VsPackage" d:Source="Project" d:ProjectName="%CurrentProject%" Path="|%CurrentProject%;PkgdefProjectOutputGroup|" />