odthoma said about 2 years ago on Fixing Assets in CSS Bundling for Rails :
I found a pretty good solution to this. I think this is a better approach than copying the fonts over.

Add this to config/initializers/assets.rb:
Rails.application.config.assets.paths << Rails.root.join('node_modules/@fortawesome/fontawesome-pro')

And then set the FontAwesome font-path sass variable to:
$fa-font-path: './webfonts';