Log Message:
www/passenger: Update to 5.3.1.

Release 5.3.1
-------------
- Fixes a regression from 5.3.0: a crash that occurs if the user that
  an application should run under, does not have a shell configured.
- Fixes a regression from 5.3.0: setting supplementary group IDs
  during user switching.

Release 5.3.0
-------------
- Vastly improves spawning error page: quick overview of where the
  problem is, and the option to drill down in extensive
  troubleshooting information.
- Fuse Panel support: fixes a crash that occurs when you shut down
  Passenger right after it fails to connect to Fuse Panel.
- [Nginx] Updates the preferred Nginx version to 1.14.0 (from 1.12.2).
- [Enterprise] Fix licensing proxy warning to refer to
  licensing_proxy_url instead of licensing_proxy.
- [Enterprise] Add new `PassengerAppLogFile` (Apache) /
  `passenger_app_log_file` (Nginx) config option to specify a file for
  app-specific logs.