fixing codecov badge

Author: heckj

README.md

@@ -3,7 +3,8 @@
 [![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fswiftviz%2FScale%2Fbadge%3Ftype%3Dswift-versions)](https://swiftpackageindex.com/swiftviz/Scale)
 [![](https://img.shields.io/endpoint?url=https%3A%2F%2Fswiftpackageindex.com%2Fapi%2Fpackages%2Fswiftviz%2FScale%2Fbadge%3Ftype%3Dplatforms)](https://swiftpackageindex.com/swiftviz/Scale)
 
-[![codecov](https://codecov.io/gh/swiftviz/Scale/branch/master/graph/badge.svg?token=fbjd3ei11P)](https://codecov.io/gh/swiftviz/Scale)
+[![codecov](https://codecov.io/gh/swiftviz/Scale/branch/main/graph/badge.svg?token=fbjd3ei11P)](https://codecov.io/gh/swiftviz/Scale)
+
 ![@heckj](https://img.shields.io/badge/[email protected]?style=flat "Twitter: @heckj")
 
 Scale and related types to support creating visualizations.