Fix coverage badge

README.md

@@ -4,7 +4,7 @@ Datafiles is a bidirectional serialization library for Python [dataclasses](http
 
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 [![AppVeyor CI](https://img.shields.io/appveyor/ci/jacebrowning/datafiles/main.svg?label=windows)](https://ci.appveyor.com/project/jacebrowning/datafiles)
-[![Codecov](https://img.shields.io/codecov/c/gh/jacebrowning/datafiles)](https://codecov.io/gh/jacebrowning/datafiles)
+[![Codecov](https://codecov.io/gh/jacebrowning/datafiles/branch/main/graph/badge.svg)](https://codecov.io/gh/jacebrowning/datafiles)
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