Signal.trap("TERM")

`Signal.trap(TERM)` to kill unicorn and serverengine processes in along with god by `kill {god_process}` command. 

I am monkey patching `#default_run` https://github.com/mojombo/god/blob/f0866e9dfaeb93cdfa1bf8d1dc51d0d17f8e194e/lib/god/cli/run.rb#L40. 
Singnal.trap is effective for both foreground and background now.