Add cache to build workflow

.github/workflows/build.yml

@@ -20,7 +20,16 @@ jobs:
       - name: Check out code into the Go module directory
         uses: actions/checkout@v1
 
+      - uses: actions/cache@v1
+        id: cache-go
+        with:
+          path: ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+          restore-keys: |
+            ${{ runner.os }}-go-
+
       - name: Download dependencies
+        if: steps.cache-go.outputs.cache-hit != 'true'
         run: go mod download
 
       - name: Test
@@ -36,6 +45,14 @@ jobs:
         with:
           node-version: 13
 
+      - uses: actions/cache@v1
+        id: cache-npm
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-node-${{ hashFiles('ui/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-node-
+
       - name: npm install dependencies
         run: |
           cd ui