feat: Cache build dependencies on GithubActnions.

.github/workflows/go.yml

@@ -27,6 +27,14 @@ jobs:
     - name: Check out code into the Go module directory
       uses: actions/checkout@v2
 
+    - name: Cache dependencies
+      uses: actions/cache@v2
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Get dependencies
       run: |
         go get -v -t -d ./...