Upgrade to rails 6 💎 (#11)

- upgraded to rails 6
- fixes various issues

config/puma.rb

@@ -1,22 +1,26 @@
 # Puma can serve each request in a thread from an internal thread pool.
-# The `threads` method setting takes two numbers a minimum and maximum.
+# The `threads` method setting takes two numbers: a minimum and maximum.
 # Any libraries that use thread pools should be configured to match
 # the maximum value specified for Puma. Default is set to 5 threads for minimum
-# and maximum, this matches the default thread size of Active Record.
+# and maximum; this matches the default thread size of Active Record.
 #
-threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }.to_i
-threads threads_count, threads_count
+max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 5 }
+min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { max_threads_count }
+threads min_threads_count, max_threads_count
 
-# Specifies the `port` that Puma will listen on to receive requests, default is 3000.
+# Specifies the `port` that Puma will listen on to receive requests; default is 3000.
 #
-port        ENV.fetch("PORT") { 3000 }
+port ENV.fetch("PORT") { 3000 }
 
 # Specifies the `environment` that Puma will run in.
 #
 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
+# Workers are forked web server processes. If using threads and workers together
 # the concurrency of the application would be max `threads` * `workers`.
 # Workers do not work on JRuby or Windows (both of which do not support
 # processes).
@@ -26,22 +30,9 @@ 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!
 
-# 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 `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, 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