Bug 1096824 - [Loop] Sign up requests might be unauthorized due to assertions expired

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1096824. Action happens at https://github.com/jaoo/firefoxos-loop-client/tree/1096824.
> "Sorry, due to problems on our side your account session has expired. Please try logging in 
> again. If the problem persist, you might need to log out from Firefox Accounts on the Settings
> App."

Much better!