html-proofer: 3.18.8 -> 5.0.8
Had to run `bundle config set force_ruby_platform true` on my machine to
avoid platform-specific dependencies (bundix doesn't like these). Maybe
there's a way to export `BUNDLE_FORCE_RUBY_PLATFORM` when the update
script is ran... not sure.
authored by Alejandro Angulo and committed by Anderson Torres b65f0cc8 37458514