Update apps.rb

--app APP is currently only noted on a couple commands but all except create need it. It's in the error message when you run without it, but also nice to have here :)
Correct typo

Changed "WARNING: pg:diagnose is only fully **suppoted** on Postgres version >= 9.2." to "WARNING: pg:diagnose is only fully **supported** on Postgres version >= 9.2. "
Merge pull request #1150 from heroku/rcross-pg-diagnose

Correct typo
Use #display for #ask_for_second_factor to flush $stdout
Merge pull request #1143 from renegadeofunk/patch-1

Update apps.rb
Merge pull request #1153 from heroku/display_ask_for_second_factor

Use #display for #ask_for_second_factor to flush $stdout