Setup a Github action for checking the cloudflared build

.github/workflows/check.yaml

@@ -0,0 +1,20 @@
+on: [push, pull_request]
+name: Check
+jobs:
+  check:
+    strategy:
+      matrix:
+        go-version: [1.15.x]
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - name: Install Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: ${{ matrix.go-version }}
+    - name: Install go-sumtype
+      run: go get github.com/BurntSushi/go-sumtype
+    - name: Checkout code
+      uses: actions/checkout@v2
+    - name: Test
+      run: make test