pry-byebug: Thread hangs

See https://github.com/deivid-rodriguez/byebug/issues/115

I have an example repo here: https://github.com/andrewfader/minimal_byebug_hang

bash-3.2$ rspec
hello
Capybara: 2.4.4
capybara-webkit: 1.6.0
Qt: 5.4.2
WebKit: 538.1
QtWebKit: 5.4.2

From: /Users/pivotal/workspace/minimal_byebug_hang_repo/spec/capybara_test_spec.rb @ line 10 :

     5:   describe 'helo' do
     6:     it 'hi' do
     7:       puts "hello"
     8:       puts page.driver.version
     9:       binding.pry
 => 10:       puts 'we aint here'
    11:     end
    12:   end
    13: end

[1] pry(#<RSpec::ExampleGroups::ATest::Helo>)> page.driver.version