Fixed NoMethodError when running rake routes

`NoMethodError: undefined method `auto_explain_threshold_in_seconds=' for ActiveRecord::Base:Class`
In config/environments/development.rb, removed line 74
  `config.active_record.auto_explain_threshold_in_seconds = 0.5`
per http://guides.rubyonrails.org/4_0_release_notes.html#active-record-notable-changes