Fix a wrong AllowedPatterns example in Rails/FindEach

This PR is fix a wrong AllowedPatterns example in `Rails/FindEach`
When specifying in the .rubocop.yml file, it is necessary to specify `AllowedPatterns: ['foo']` instead of `AllowedPatterns: [/foo/]`.

Follow up: rubocop/rubocop-rspec#1395

The test code was also modified to match the actual behavior as mentioned in rubocop/rubocop-rspec#1396 (comment) .

Author: ydah

lib/rubocop/cop/rails/find_each.rb

@@ -17,7 +17,7 @@ module Rails
       #   # good
       #   User.order(:foo).each
       #
-      # @example AllowedPattern: [/order/]
+      # @example AllowedPattern: ['order']
       #   # good
       #   User.order(:foo).each
       class FindEach < Base

spec/rubocop/cop/rails/find_each_spec.rb

@@ -142,7 +142,7 @@ class C < ActiveRecord::Base
   end
 
   context 'allowed patterns' do
-    let(:cop_config) { { 'AllowedMethods' => [], 'AllowedPatterns' => [/order/, /lock/], 'IgnoredMethods' => [] } }
+    let(:cop_config) { { 'AllowedMethods' => [], 'AllowedPatterns' => %w[order lock], 'IgnoredMethods' => [] } }
 
     it 'does not register an offense when using order(...) earlier' do
       expect_no_offenses('User.order(:name).each { |u| u.something }')