Unity: ignore Visual Studio 2015 cache directory

Since the version 5.2, Unity has used Visual Studio 2015 instead of MonoDevelop as default script editor in Windows.
This change may be helpful for Unity developers who use the recent version of Unity in Windows.

Unity.gitignore

@@ -5,6 +5,9 @@
 /[Bb]uilds/
 /Assets/AssetStoreTools*
 
+# Visual Studio 2015 cache directory
+/.vs/
+
 # Autogenerated VS/MD/Consulo solution and project files
 ExportedObj/
 .consulo/