hubot-asana requires @assignments to be lowercase

Because the code does a `toLowerCase()` on the names coming from API data (https://github.com/idpro/hubot-asana/blob/master/asana.coffee#L64), Hubot command necessarily has to take a lowercase form or the equality doesn't return true (https://github.com/idpro/hubot-asana/blob/master/asana.coffee#L65)

If you `toLowerCase()` input data as well, that should not longer be necessary.