Fix appid validation regression.

When building, the app id is validated, and, according to the rules
previously in place, may not contain hyphens.

However, this was allowed in the 2.* SDK and there are now existing
apps using hyphens for their IDs which cannot be changed due to
Apple AppStore restrictions.

This is a regression!
Please pull this in asap, as it is mandatory for building our app with the 3.* SDKs.