Fixed copyright symbol in testgles2 program.

test/testgles2.c

@@ -1,5 +1,5 @@
 /*
-  Copyright (r) 1997-2017 Sam Lantinga <[email protected]>
+  Copyright (C) 1997-2017 Sam Lantinga <[email protected]>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages