Bump rails to 5.2 and update rubocop

config/puma.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Puma can serve each request in a thread from an internal thread pool.
 # The `threads` method setting takes two numbers: a minimum and maximum.
 # Any libraries that use thread pools should be configured to match
@@ -15,6 +17,9 @@ port        ENV.fetch('PORT') { 3000 }
 #
 environment ENV.fetch('RAILS_ENV') { 'development' }
 
+# Specifies the `pidfile` that Puma will use.
+pidfile ENV.fetch('PIDFILE') { 'tmp/pids/server.pid' }
+
 # Specifies the number of `workers` to boot in clustered mode.
 # Workers are forked webserver processes. If using threads and workers together
 # the concurrency of the application would be max `threads` * `workers`.
@@ -26,31 +31,9 @@ environment ENV.fetch('RAILS_ENV') { 'development' }
 # Use the `preload_app!` method when specifying a `workers` number.
 # This directive tells Puma to first boot the application and load code
 # before forking the application. This takes advantage of Copy On Write
-# process behavior so workers use less memory. If you use this option
-# you need to make sure to reconnect any threads in the `on_worker_boot`
-# block.
+# process behavior so workers use less memory.
 #
 # preload_app!
 
-# If you are preloading your application and using Active Record, it's
-# recommended that you close any connections to the database before workers
-# are forked to prevent connection leakage.
-#
-# before_fork do
-#   ActiveRecord::Base.connection_pool.disconnect! if defined?(ActiveRecord)
-# end
-
-# The code in the `on_worker_boot` will be called if you are using
-# clustered mode by specifying a number of `workers`. After each worker
-# process is booted, this block will be run. If you are using the `preload_app!`
-# option, you will want to use this block to reconnect to any threads
-# or connections that may have been created at application boot, as Ruby
-# cannot share connections between processes.
-#
-# on_worker_boot do
-#   ActiveRecord::Base.establish_connection if defined?(ActiveRecord)
-# end
-#
-
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart