fix build badge (#59)

Author: morningvera

README.md

@@ -1,6 +1,7 @@
 # Polygon Go Client
 
 <!-- todo: add a codecov badge -->
+<!-- todo: figure out a way to show all build statuses -->
 
 [![Docs][doc-img]][doc] [![Build][build-img]][build]
 
@@ -97,5 +98,5 @@ For now, we're generally not accepting pull requests from outside contributors b
 
 [doc-img]: https://pkg.go.dev/badge/github.com/polygon-io/client-go
 [doc]: https://pkg.go.dev/github.com/polygon-io/client-go
-[build-img]: https://github.com/polygon-io/client-go/workflows/badge.svg
+[build-img]: https://github.com/polygon-io/client-go/actions/workflows/test.yml/badge.svg
 [build]: https://github.com/polygon-io/client-go/actions