Switch to Codecov in the README too

README.md

@@ -115,12 +115,12 @@ issue](https://github.com/rmccue/Requests/issues/new)!
 Testing
 -------
 [![Build Status](https://secure.travis-ci.org/rmccue/Requests.png?branch=master)](http://travis-ci.org/rmccue/Requests)
-[![Coverage Status](https://coveralls.io/repos/rmccue/Requests/badge.png?branch=master)][coveralls]
+[![codecov.io](http://codecov.io/github/rmccue/Requests/coverage.svg?branch=master)](http://codecov.io/github/rmccue/Requests?branch=master)
 
 Requests strives to have 100% code-coverage of the library with an extensive
-set of tests. We're not quite there yet, but [we're getting close][coveralls].
+set of tests. We're not quite there yet, but [we're getting close][codecov].
 
-[coveralls]: https://coveralls.io/r/rmccue/Requests?branch=master
+[codecov]: http://codecov.io/github/rmccue/Requests
 
 To run the test suite, first check that you have the [PHP
 JSON extension ](http://php.net/manual/en/book.json.php) enabled. Then