`brew cask-tests` collected the test results in an improper way so that it reports a false success in certain situations.
Specially, the session under BrewTestBot always reports success regardless of the test status.
With this update, the exit code of `brew cask-tests` is 1 when the test fails, and then CI preperly works.
This hack has been in Homebrew Cask for more than two years
(since 51f93e6dc9c3da4ab2118459ea95e45c104386ec), and it originated even
earlier (6d2f7bc55af0b2aa915b2396d213e30a4446256c).
Cask tests apparently aren't even run on Travis anymore,
so this can be safely removed.
