update npm in CI

.github/workflows/main.yml

@@ -15,6 +15,10 @@ jobs:
       uses: actions/setup-node@v1
       with:
         node-version: 10.x
+
+    - name: Update npm
+      run: npm install -g npm@7
+
     - name: npm install and build
       run: |
         npm install

.github/workflows/test.yml

@@ -24,6 +24,9 @@ jobs:
         sudo apt-get update
         sudo apt-get install -y chromium-browser firefox
 
+    - name: Update npm
+      run: npm install -g npm@7
+
     - name: Install the project
       run: npm install