Change MELPA link to MELPA Stable

Because stability is cool

README.md

@@ -7,7 +7,7 @@ Gimme some ido... everywhere! This package replaces stock emacs
 completion with ido completion wherever it is possible to do so
 without breaking things.
 
-Get it from MELPA: http://melpa.org/#/ido-ubiquitous
+Get it from MELPA: https://stable.melpa.org/#/ido-ubiquitous
 
 ## Version 3.0 changes ##