reenable coverage (JuliaDiff#505)

Needs support in Julia base, so only works on nightly.

Author: simeonschaub

.github/workflows/JuliaNightly.yml

@@ -41,3 +41,20 @@ jobs:
             ${{ runner.os }}-
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          flag-name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }}
+          parallel: true
+          path-to-lcov: lcov.info
+
+  finish:
+    name: Coveralls Finished
+    needs: test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: coverallsapp/github-action@master
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          parallel-finished: true

README.md

@@ -4,6 +4,7 @@
 
 [![CI](https://github.com/JuliaDiff/ChainRules.jl/workflows/CI/badge.svg?branch=master)](https://github.com/JuliaDiff/ChainRules.jl/actions?query=workflow%3ACI)
 [![Travis](https://travis-ci.org/JuliaDiff/ChainRules.jl.svg?branch=master)](https://travis-ci.org/JuliaDiff/ChainRules.jl)
+[![Coveralls](https://coveralls.io/repos/github/JuliaDiff/ChainRules.jl/badge.svg?branch=master)](https://coveralls.io/github/JuliaDiff/ChainRules.jl?branch=master)
 [![PkgEval](https://juliaci.github.io/NanosoldierReports/pkgeval_badges/C/ChainRules.svg)](https://juliaci.github.io/NanosoldierReports/pkgeval_badges/report.html)
 [![Code Style: Blue](https://img.shields.io/badge/code%20style-blue-4495d1.svg)](https://github.com/invenia/BlueStyle)
 [![ColPrac: Contributor's Guide on Collaborative Practices for Community Packages](https://img.shields.io/badge/ColPrac-Contributor's%20Guide-blueviolet)](https://github.com/SciML/ColPrac)