Fix GitHub Actions (#110)

https://github.com/codecov/codecov-ruby/pull/107/checks?check_run_id=1412253301

Author: AlexWayfer

.github/workflows/ruby.yml

@@ -9,7 +9,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Set up Ruby
-      uses: ruby/setup-ruby@ec106b438a1ff6ff109590de34ddc62c540232e0
+      uses: ruby/setup-ruby@v1
       with:
         ruby-version: 2.6
     - name: Install dependencies