Better way to kill process (#569)

As per #293 (comment), this change still keeps the desired behaviour of killing the process on CTRL-C, but it gives parent processes a chance to clean up.

lib/ui/baseUI.js

@@ -22,7 +22,7 @@ var UI = module.exports = function (opt) {
 
   // Terminate process on SIGINT (which will call process.on('exit') in return)
   this.rl.on('SIGINT', function () {
-    process.exit(0);
+    process.kill(process.pid, 'SIGINT');
   });
 };