use already installed nodejs

and setup/actions are having issues because we can't reach nodejs
servers:
actions/setup-node#132

And it looks like the default ubuntu version already have nodejs:
https://github.com/actions/virtual-environments/blob/efe1d6eb1a6e5820fbd3d1036f9b0a56beb53a09/images/linux/Ubuntu1804-README.md

.github/workflows/deploy.yaml

@@ -22,9 +22,6 @@ jobs:
       with:
         submodules: true  # Fetch Hugo themes
         fetch-depth: 0    # Fetch all history for .GitInfo and .Lastmod
-    - uses: actions/setup-node@v1
-      with:
-        node-version: '12.x'
     - run: npm install -g postcss-cli autoprefixer
     - name: Setup Hugo
       uses: peaceiris/actions-hugo@v2