userdiff.c: add C# async keyword in diff pattern

Currently C# async methods are not shown in diff hunk headers. I just
added the async keyword to the csharp method pattern so that they are
properly detected.

Signed-off-by: Thomas Levesque <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: thomaslevesque

userdiff.c

@@ -138,7 +138,7 @@ PATTERNS("csharp",
 	 /* Keywords */
 	 "!^[ \t]*(do|while|for|if|else|instanceof|new|return|switch|case|throw|catch|using)\n"
 	 /* Methods and constructors */
-	 "^[ \t]*(((static|public|internal|private|protected|new|virtual|sealed|override|unsafe)[ \t]+)*[][<>@.~_[:alnum:]]+[ \t]+[<>@._[:alnum:]]+[ \t]*\\(.*\\))[ \t]*$\n"
+	 "^[ \t]*(((static|public|internal|private|protected|new|virtual|sealed|override|unsafe|async)[ \t]+)*[][<>@.~_[:alnum:]]+[ \t]+[<>@._[:alnum:]]+[ \t]*\\(.*\\))[ \t]*$\n"
 	 /* Properties */
 	 "^[ \t]*(((static|public|internal|private|protected|new|virtual|sealed|override|unsafe)[ \t]+)*[][<>@.~_[:alnum:]]+[ \t]+[@._[:alnum:]]+)[ \t]*$\n"
 	 /* Type definitions */