Fix tw in vim modeline.

js/src/jsfun.c

@@ -1,5 +1,5 @@
 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
- * vim: set ts=8 sw=4 et tw=80:
+ * vim: set ts=8 sw=4 et tw=78:
  *
  * ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1