Add bigserial as a native database type for MySQL adapter

config/initializers/ar_native_database_types.rb

+require 'active_record/connection_adapters/abstract_mysql_adapter'
+
+module ActiveRecord
+  module ConnectionAdapters
+    class AbstractMysqlAdapter
+      NATIVE_DATABASE_TYPES.merge!(
+        bigserial:  { name: 'bigint(20) auto_increment PRIMARY KEY' }
+      )
+    end
+  end
+end