Add GPA badge

Author: Emmanouil Konstantinidis

README.md

@@ -1,9 +1,12 @@
 # Gitify
 [![travis][travis-image]][travis-url]
+[![cc-gpa][cc-gpa-image]][cc-gpa-url]
 [![cc-coverage][cc-coverage-image]][cc-coverage-url]
 
 [travis-image]: https://travis-ci.org/ekonstantinidis/gitify.svg?branch=master
 [travis-url]: https://travis-ci.org/ekonstantinidis/gitify
+[cc-gpa-image]: https://codeclimate.com/github/ekonstantinidis/gitify/badges/gpa.svg
+[cc-gpa-url]: https://codeclimate.com/github/ekonstantinidis/gitify
 [cc-coverage-image]: https://codeclimate.com/github/ekonstantinidis/gitify/badges/coverage.svg
 [cc-coverage-url]: https://codeclimate.com/github/ekonstantinidis/gitify/coverage