Respond if it's a holiday

Fixes https://github.com/bugsnag/bugsnag-support-hubot/issues/5
Fun fact, coffeescript supports multi-line strings which are great for stuff like this.

For example:

```
supportMessage =
  """
  Hey #{name}! Thanks for stopping by. Unfortunately, it looks like it's outside of business hours in San Francisco, so a human may not respond right now.
  Feel free to send an e-mail with your questions to support@bugsnag.com in the mean time, or come back from 10am-7pm PST.
  I'd also recommend checking out our docs page, we may have already answered your question: https://www.bugsnag.com/docs/
  """
```