Fix MELPA Stable badge

Fixes #157.

README.md

@@ -1,6 +1,6 @@
 # ido-completing-read+ (formerly ido-ubiquitous) #
 
-[![MELPA Stable](https://stable.melpa.org/packages/ido-ubiquitous-badge.svg)](https://stable.melpa.org/#/ido-ubiquitous)
+[![MELPA Stable](https://stable.melpa.org/packages/ido-completing-read+-badge.svg)](https://stable.melpa.org/#/ido-completing-read%2B)
 [![Join the chat at https://gitter.im/DarwinAwardWinner/ido-ubiquitous](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/DarwinAwardWinner/ido-ubiquitous?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![Build Status](https://travis-ci.org/DarwinAwardWinner/ido-completing-read-plus.svg?branch=master)](https://travis-ci.org/DarwinAwardWinner/ido-completing-read-plus)
 [![Coverage Status](https://coveralls.io/repos/github/DarwinAwardWinner/ido-completing-read-plus/badge.svg?branch=master)](https://coveralls.io/github/DarwinAwardWinner/ido-completing-read-plus?branch=master)