Update ruby setup action (#56)

* Change action to use ruby/ruby-setup instead of actions/ruby-setup

* Remove 2.4 from testing matrix

Author: adamrdavid

.github/workflows/build.yml

@@ -7,12 +7,12 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        ruby: ['2.4', '2.5', '2.6', '2.7.x', '2.x']
+        ruby: ['2.5', '2.6', '2.7']
     name: Test ruby v${{ matrix.ruby }} support
     steps:
     - uses: actions/checkout@v1
     - name: Set up Ruby ${{ matrix.ruby }}
-      uses: actions/setup-ruby@v1
+      uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
     - name: Build with dependencies