Add step to main Github actions workflow which will cache node module…

…s files

.github/workflows/main.yml

@@ -13,6 +13,15 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - name: Cache node modules
+        uses: actions/cache@v2
+        with:
+          path: ~/.npm
+          key: ${{ runner.os }}-build-${{ hashFiles('**/package-lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+
       - name: Install dependencies
         run: npm ci