Merge pull request #1108 from shadowsocks/try-github-action

Add github action workflow configure file.

.github/workflows/main.yml

@@ -0,0 +1,14 @@
+name: CI
+
+on: [push,pull_request]
+
+jobs:
+  build:
+
+    runs-on: macOS-10.14
+    
+    steps:
+    - uses: actions/checkout@v1
+    - name: Build
+      run: |
+        set -o pipefail && xcodebuild test -workspace ShadowsocksX-NG.xcworkspace -scheme ShadowsocksX-NG|xcpretty