Rails 6 deprecation warning: Logger don't need to call #after_initialize directly anymore

[bwillis]

When running with Rails 6, we get a deprecation warning:

DEPRECATION WARNING: Logger don't need to call #after_initialize directly anymore. It will be deprecated without replacement in Rails 6.1. (called from new at /focus/config/environments/development.rb:70)

This is due to this call in the logger constructor.