OK, this was _not_ a good fix. It breaks travis. (see below). Removing it, think of something better.

> PHP Fatal error:  Uncaught exception 'RuntimeException' with message
'Failed to start the session because headers have already been sent by
"/home/travis/build/bolt/bolt/app/src/Bolt/Database/IntegrityChecker.php
" at line 63.' in
/home/travis/build/bolt/bolt/vendor/symfony/http-foundation/Symfony/Comp
onent/HttpFoundation/Session/Storage/NativeSessionStorage.php:144