Prevent ^C triggering a DeadClient error

Closes #252

README.md

@@ -325,6 +325,8 @@ Include as much information as possible. For example:
     and in general doesn't seem to be worth the trouble at the moment.
     It can be reconsidered in the future when PhantomJS has upgraded its
     WebKit version. [Issue #176, #223]
+*   Run phantomjs in a new process group so ^C doesn't trigger a
+    DeadClient error [Issue #252]
 
 ### 1.1.0 ###
 

lib/capybara/poltergeist/client.rb

@@ -38,7 +38,7 @@ module Capybara::Poltergeist
       }
 
       redirect_stdout(write) do
-        @pid = Process.spawn(*command.map(&:to_s))
+        @pid = Process.spawn(*command.map(&:to_s), pgroup: true)
       end
     end