Set the NODE_ENV variable when running yarn

The assets precompilation task runs yarn with NODE_ENV=production,
before this change yarn would install a different set of packages, with
this change the run from the assets precompilation is idempotent

site-cookbooks/kosmos-mastodon/recipes/default.rb

@@ -174,7 +174,7 @@ application mastodon_path do
   end
 
   execute "yarn install" do
-    environment "HOME" => mastodon_path
+    environment "HOME" => mastodon_path, "NODE_ENV" => "production"
     user mastodon_user
     cwd mastodon_path
     command "yarn install --pure-lockfile"