add GitHub Actions workflow

.github/workflows/push.yml

@@ -0,0 +1,50 @@
+name: 'push'
+
+on: [push, pull_request]
+
+jobs:
+
+  test:
+    strategy:
+      matrix:
+        os: [ ubuntu, windows, macOS ]
+        go: [ 1.12.x, 1.13.x ]
+
+    runs-on: ${{ matrix.os }}-latest
+
+    steps:
+
+    - name: Setup go
+      uses: actions/setup-go@v1
+      with:
+        go-version: ${{ matrix.go }}
+
+    - run: go get -v github.com/kyoh86/richgo@v0.3.3
+      env:
+        GO111MODULE: on
+
+    - uses: actions/checkout@v1
+
+    - name: run tests
+      shell: bash
+      run: $HOME/go/bin/richgo test -v ./...
+      env:
+        GO111MODULE: on
+
+    - name: check formatting
+      if: matrix.os != 'windows'
+      run: diff -u <(echo -n) <(gofmt -d -s .)
+
+    - name: build
+      run: |
+        cd cobra
+        go build
+      env:
+        GO111MODULE: on
+
+    - name: go vet
+      if: matrix.os != 'windows'
+      run: |
+        if [ -z $NOVET ]; then
+          diff -u <(echo -n) <(go vet . 2>&1 | grep -vE 'ExampleCommand|bash_completions.*Fprint');
+        fi