Use build cache

.github/workflows/go.yml

@@ -15,6 +15,16 @@ jobs:
         go-version: ${{ matrix.go-version }}
     - name: checkout
       uses: actions/checkout@v2
+    - uses: actions/cache@v2
+      with:
+        path: |
+          ~/go/pkg/mod
+          ~/.cache/go-build
+          ~/Library/Caches/go-build
+          '%LocalAppData%\go-build'
+      key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+      restore-keys: |
+        ${{ runner.os }}-go-
     - name: simple test
       run: go test -v ./ -count=1
     - name: test with GC pressure