Incompatible with v3 of `connection_pool`

[G-Rath]

v3 changed ConnectionPool to take keyword args rather than positional args, which breaks

react-rails/lib/react/server_rendering.rb

Line 19 in 28ee689

@pool = ConnectionPool.new(options) { renderer.new(renderer_options) }

I've not dug deeper into this yet so that might not be the only change that is needed - I'd consider doing a new version locking connection_pool to <= 2 for the time being