Reenable installation for all users

Author: shana

src/GitHub.VisualStudio/source.extension.vsixmanifest

@@ -10,7 +10,7 @@
     <PreviewImage>Resources\preview_200x200.png</PreviewImage>
     <Tags>GitHub git github.com team explorer</Tags>
   </Metadata>
-  <Installation>
+  <Installation AllUsers="true">
     <InstallationTarget Id="Microsoft.VisualStudio.Community" Version="[14.0,]" />
   </Installation>
   <Dependencies>