README: update badges

- add stackage badges
- replace broken travis badge by GHA badge

Author: andreasabel

README.md

@@ -1,4 +1,8 @@
-The `parallel` Package  [![Hackage](https://img.shields.io/hackage/v/parallel.svg)](https://hackage.haskell.org/package/parallel) [![Build Status](https://travis-ci.org/haskell/parallel.svg)](https://travis-ci.org/haskell/parallel)
+The `parallel` Package
+[![Hackage version](https://img.shields.io/hackage/v/parallel.svg?label=Hackage&color=informational)](http://hackage.haskell.org/package/parallel)
+[![Stackage Nightly version](https://stackage.org/package/parallel/badge/nightly)](https://stackage.org/nightly/package/parallel)
+[![Stackage LTS version](https://www.stackage.org/package/parallel/badge/lts?label=Stackage)](https://www.stackage.org/package/parallel)
+[![Build status](https://github.com/haskell/parallel/workflows/Haskell-CI/badge.svg)](https://github.com/haskell/parallel/actions)
 ======================
 
 See [`parallel` on Hackage](http://hackage.haskell.org/package/parallel) for more information.