fix coveralls link

README.md

@@ -3,7 +3,7 @@ c-ares
 
 [![Build Status](https://api.cirrus-ci.com/github/c-ares/c-ares.svg)](https://cirrus-ci.com/github/c-ares/c-ares)
 [![Windows Build Status](https://ci.appveyor.com/api/projects/status/aevgc5914tm72pvs/branch/master?svg=true)](https://ci.appveyor.com/project/c-ares/c-ares/branch/master)
-[![Coverage Status](https://coveralls.io/repos/c-ares/c-ares/badge.svg?branch=master&service=github)](https://coveralls.io/github/c-ares/c-ares?branch=master)
+[![Coverage Status](https://coveralls.io/repos/github/c-ares/c-ares/badge.svg)](https://coveralls.io/github/c-ares/c-ares)
 [![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/291/badge)](https://bestpractices.coreinfrastructure.org/projects/291)
 [![Fuzzing Status](https://oss-fuzz-build-logs.storage.googleapis.com/badges/c-ares.svg)](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:c-ares)
 [![Releases](https://coderelease.io/badge/c-ares/c-ares)](https://coderelease.io/github/repository/c-ares/c-ares)