trying to behave in here and use 2 spaces instead of 4 ;)
moved invite_code to env var
don't render the sign-up form at all if invite code is incorrect
no default value for invite code
this should fix the test #84
ENV statements need a value
doc for CONVOS_INVITE_CODE
Merge pull request #84 from DominikTo/env-invite-code

Moved invite code to env var