Bump to v2.0.0.b7, remove non existing files

Hi Evan,

thanks for writing puma!
Wanted to use the newest version 2.0.0.b7 to allow restarting with pumactl but it's net yet fully deployed and I got a failure message for the earlier version:
    
/bundler/gems/puma-deddeedccb24 did not have a valid gemspec.
This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
If you need to use this package without installing it from a gem repository, please contact ["evan@phx.io"] and ask them to modify their .gemspec so it can work with `gem build`.
The validation message from Rubygems was:
  ["tools/jungle/puma", "tools/jungle/run-puma"] are not files