add support for `grunt-contrib-watch`
currently I don't call done to leave the express server running. Using grunt-contrib-watch causes errors like EADDRINUSE, Address already in use.
grunt-express is doing some interesting stuff with restarting express servers. Having a separate task that just calls this.async().
I have this working with a basic express server here: https://github.com/shanejonas/chalice-docs/blob/master/Gruntfile.coffee with regarde and a custom express-server task.
FWIW grunt-regarde is on it's way to deprecation gruntjs/grunt-contrib-livereload#27 gruntjs/grunt-contrib-livereload#32 . grunt-contrib-watch will get a lot better.
Also: https://github.com/gruntjs/grunt-contrib-watch/issues/45