Always unlock the lockfile when killing the app.

Otherwise, we have a deadlock whenever the lock is forced: the app
will be restarted, and will find the lockfile is already there so it won't be
able to lock/unlock it. The supervisor will have the same problem.
So the solution is that, whenever we kill the app, that is the lock owner, we also unlock the file.

src/application.coffee

@@ -110,6 +110,8 @@ exports.kill = kill = (app) ->
 		if statusCode is '404'
 			return
 		throw err
+	.tap ->
+		lockFile.unlockAsync(lockPath(app))
 	.tap ->
 		logSystemEvent(logTypes.stopAppSuccess, app)
 		app.containerId = null