Fixet typo in a comment. (changeset 1249258)

Src/Compilers/CSharp/Source/LanguageVersion.cs

@@ -54,7 +54,7 @@ public enum LanguageVersion
         CSharp6 = 6,
 
         /// <summary>
-        /// C# language version 6.0 + experimentatl features. 
+        /// C# language version 6.0 + experimental features. 
         /// </summary>
         Experimental = 7,
     }