[chore] add 'npm' cache for actions/setup-node in .github/workflows (#190)

Fixes #192

Author: oscard0m

.github/workflows/ci.yml

@@ -5,7 +5,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        node-version: [ '10', '12', '14' ]
+        node-version: ["10", "12", "14"]
         os: [ubuntu-latest, windows-latest]
     name: Test on Node v${{ matrix.node-version }} on ${{ matrix.os }}
     steps:
@@ -14,6 +14,7 @@ jobs:
         uses: actions/setup-node@v2
         with:
           node-version: ${{ matrix.node-version }}
+          cache: npm
       - run: npm install
       - run: npm run all
         env: