Enable puma clustered (RefugeRestrooms#654)

Enable puma clustered mode to process more requests and reduce latency

config/puma.rb

@@ -21,14 +21,7 @@
 # Workers do not work on JRuby or Windows (both of which do not support
 # processes).
 #
-# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
-
-# 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.
-#
-# preload_app!
+workers ENV.fetch("WEB_CONCURRENCY") { 3 }
 
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart