Setup NPM with an empty package.json file

Note that, even if we're excluding the `node_modules/` folder from
version control, we aren't adding it to Capistrano's shared folders
because, when `node_modules` is a symbolic link, NPM removes it when
running `npm install`.

.dockerignore

@@ -24,6 +24,7 @@ public/tenants/*/sitemap.xml
 public/assets/
 public/machine_learning/data/
 public/tenants/*/machine_learning/data/
+node_modules/
 
 # Bundler config, cache and gemsets
 **/.bundle/