use actions/cache

.github/workflows/go.yml

@@ -19,6 +19,15 @@ jobs:
     steps:
     - uses: actions/checkout@v2
 
+    - uses: actions/cache@v2
+      with:
+        path: |
+          ~/.cache/go-build
+          ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Setup redis
       uses: shogo82148/actions-setup-redis@v1
       with: