README: Wrap GitHub badges to be one line for each badges.

Apparently, we no longer need to do the hacky no-line-wrapping thing
we were doing for these to work.

README.md

@@ -19,7 +19,12 @@ missed-message emails, desktop apps, and much more.
 Further information on the Zulip project and its features can be found
 at <https://www.zulip.org>.
 
-[![Build Status](https://travis-ci.org/zulip/zulip.svg?branch=master)](https://travis-ci.org/zulip/zulip) [![Coverage Status](https://img.shields.io/codecov/c/github/zulip/zulip.svg)](https://codecov.io/gh/zulip/zulip) [![Mypy coverage](https://img.shields.io/badge/mypy-100%25-green.svg)](http://blog.zulip.org/2016/10/13/static-types-in-python-oh-mypy/) [![docs](https://readthedocs.org/projects/zulip/badge/?version=latest)](http://zulip.readthedocs.io/en/latest/) [![Zulip chat](https://img.shields.io/badge/zulip-join_chat-brightgreen.svg)](https://chat.zulip.org) [![Twitter](https://img.shields.io/badge/twitter-@zulip-blue.svg?style=flat)](http://twitter.com/zulip)
+[![Build Status](https://travis-ci.org/zulip/zulip.svg?branch=master)](https://travis-ci.org/zulip/zulip)
+[![Coverage Status](https://img.shields.io/codecov/c/github/zulip/zulip.svg)](https://codecov.io/gh/zulip/zulip)
+[![Mypy coverage](https://img.shields.io/badge/mypy-100%25-green.svg)](http://blog.zulip.org/2016/10/13/static-types-in-python-oh-mypy/)
+[![docs](https://readthedocs.org/projects/zulip/badge/?version=latest)](http://zulip.readthedocs.io/en/latest/)
+[![Zulip chat](https://img.shields.io/badge/zulip-join_chat-brightgreen.svg)](https://chat.zulip.org)
+[![Twitter](https://img.shields.io/badge/twitter-@zulip-blue.svg?style=flat)](http://twitter.com/zulip)
 
 ## Community