contrib: Add script name to usage error in gen_wcwidth.py

contrib/ChangeLog:

	* unicode/gen_wcwidth.py: Add sys.argv[0] to usage error.

contrib/unicode/gen_wcwidth.py

@@ -22,7 +22,7 @@
 import os
 
 if len(sys.argv) != 2:
-    print("usage: %s <unicode version>", file=sys.stderr)
+    print("usage: %s <unicode version>" % sys.argv[0], file=sys.stderr)
     sys.exit(1)
 unicode_version = sys.argv[1]