Update MELPA badge

Author: Wilfred

README.md

@@ -3,7 +3,7 @@
 Deadgrep is the fast, beautiful text search that your Emacs
 deserves.
 
- [![Coverage Status](https://coveralls.io/repos/github/Wilfred/deadgrep/badge.svg?branch=master)](https://coveralls.io/github/Wilfred/deadgrep?branch=master) [![MELPA](http://www.melpa.org/packages/deadgrep-badge.svg)](http://www.melpa.org/#/deadgrep)
+[![Coverage Status](https://coveralls.io/repos/github/Wilfred/deadgrep/badge.svg?branch=master)](https://coveralls.io/github/Wilfred/deadgrep?branch=master) [![MELPA](https://melpa.org/packages/deadgrep-badge.svg)](https://melpa.org/#/deadgrep)
 
 ![screenshot](docs/deadgrep_screenshot.png)