enh: Enhancing badges in readME (#2133)

- Removing `CodeCOV`.
- Addition of `Mailing List`

README.md

@@ -4,8 +4,8 @@
 
 [![Gitter](https://img.shields.io/badge/chat-on%20gitter-ff006f.svg?style=flat-square)](https://gitter.im/fossasia/badgeyay)
 [![Codacy Badge](https://api.codacy.com/project/badge/Grade/1ac554483fac462797ffa5a8b9adf2fa?style=flat-square)](https://www.codacy.com/app/fossasia/badgeyay)
-[![Travis branch](https://api.travis-ci.org/fossasia/badgeyay.svg?branch=development&style=flat-square)](https://travis-ci.org/fossasia/badgeyay)
-[![Codecov branch](https://codecov.io/gh/fossasia/badgeyay/branch/development/graph/badge.svg?style=flat-square)](https://codecov.io/gh/fossasia/badgeyay)
+[![Build Status](https://api.travis-ci.org/fossasia/badgeyay.svg?branch=development&style=flat-square)](https://travis-ci.org/fossasia/badgeyay)
+[![Mailing](https://img.shields.io/badge/Mailing-List-red.svg)](https://groups.google.com/forum/#!forum/open-event)
 
 > **Badgeyay provides an interface to event organizers for generating badges of events from concerts to conferences and meet-ups.**