Compress HTML files after ActionDispatch::Static processing

By ensurring we compress HTML files after it, we avoid duplicated work.

That is because ActionDispatch serve static assets and it already supports compressing them. Rack Deflate will try to compress it again.

See the last part of this:

• https://schneems.com/2017/11/08/80-smaller-rails-footprint-with-rack-deflate/

Part of #101 (closed)