dependency fixes

.github/workflows/extension-build.js.yml

@@ -1,6 +1,8 @@
 # This workflow will do a clean install of node dependencies, build the source code and run tests across different versions of node
 # For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
 
+# Also uses `python2` to build the webextension
+
 name: Node.js CI
 
 on:
@@ -24,7 +26,10 @@ jobs:
       uses: actions/setup-node@v1
       with:
         node-version: ${{ matrix.node-version }}
-    - run: yarn
+    - name: Install dependencies
+      run: |
+        sudo apt-get install python2
+        yarn
     - run: npm run build
     - run: npm run 
     - run: npm run build:webext