add service=github to the coveralls badge

README.md

@@ -3,7 +3,7 @@
 ## A Wrapper for the Mastodon API.
 
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+[![Coverage Status](https://coveralls.io/repos/github/pwoolcoc/elefren/badge.svg?branch=master&service=github)](https://coveralls.io/github/pwoolcoc/elefren?branch=master)
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