github workflows: use go mod

.github/workflows/build.yml

@@ -20,12 +20,13 @@ jobs:
         uses: actions/setup-go@v3
         with:
           go-version: 1.15
+          cache: true
 
-      - name: Go Get
+      - name: Download dependencies
-        run: go get -d -u
+        run: go mod download
 
-      - name: Go Build
+      - name: Build
         run: go build -v
 
-      - name: Go Test
+      - name: Test
         run: go test -v