dir-locals: Use https for bug references

We've been using https for web references for some time now.

ChangeLog:

	* .dir-locals.el (bug-reference-url-format): Use https.

Author: Richard Earnshaw

.dir-locals.el

@@ -17,7 +17,7 @@
 ((tcl-mode . ((tcl-indent-level . 4)
 	      (tcl-continued-indent-level . 4)
 	      (indent-tabs-mode . t)))
- (nil . ((bug-reference-url-format . "http://gcc.gnu.org/PR%s")))
+ (nil . ((bug-reference-url-format . "https://gcc.gnu.org/PR%s")))
  (c-mode . ((c-file-style . "GNU")
 	    (indent-tabs-mode . t)
 	    (fill-column . 79))))