First draft of GitHub Action (#309)

This does not run the integration tests.

https://github.com/zmap/zgrab2/pull/309

.github/workflows/build.yml

@@ -0,0 +1,19 @@
+name: ZGrab2 build action
+on: [push, pull_request]
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Set up Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: 1.16
+
+      - name: Check out source
+        uses: actions/checkout@v2
+
+      - name: Build
+        run: |
+          go get -t ./...
+          make