Switch Travis and Coveralls to free / open-source version. (#121)

* Switch Coveralls to free / open-source version.

* Add Travis build status badge.

Author: scouten

.travis.yml

@@ -12,7 +12,7 @@ env:
 script:
   - mix deps.get
   - mix format --check-formatted
-  - mix coveralls.travis --pro
+  - mix coveralls.travis
   - mix credo
 
 branches:

README.md

@@ -1,6 +1,6 @@
 # Xgit
 
-Pure Elixir native implementation of git [![Coverage Status](https://coveralls.io/repos/github/scouten/xgit/badge.svg?t=xE9sgP)](https://coveralls.io/github/scouten/xgit)
+Pure Elixir native implementation of git [![Build Status](https://travis-ci.org/elixir-git/xgit.svg?branch=master)](https://travis-ci.org/elixir-git/xgit) [![Coverage Status](https://coveralls.io/repos/github/elixir-git/xgit/badge.svg?branch=master)](https://coveralls.io/github/elixir-git/xgit?branch=master)
 
 
 ## WORK IN PROGRESS