github/workflows: use actions/cache

Author: zchee

.github/workflows/test.yml

@@ -40,6 +40,17 @@ jobs:
       with:
         fetch-depth: 2
 
+    - uses: actions/cache@v2
+      with:
+        path: |
+          ~/go/pkg/mod              # Module download cache
+          ~/.cache/go-build         # Build cache (Linux)
+          ~/Library/Caches/go-build # Build cache (Mac)
+          '%LocalAppData%\go-build' # Build cache (Windows)
+        key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-go-
+
     - name: Install nvim binary
       uses: rhysd/action-setup-vim@v1
       with: