add support for Uno

Uno is a fast, native dialect of C#, that includes a lot of
specialized functionality for graphics programming.

https://www.fusetools.com/learn/uno

lib/linguist/languages.yml

@@ -3591,6 +3591,13 @@ Unity3D Asset:
   - .unity
   tm_scope: source.yaml
 
+Uno:
+  type: programming
+  extensions:
+  - .uno
+  ace_mode: csharp
+  tm_scope: source.cs
+
 UnrealScript:
   type: programming
   color: "#a54c4d"