fix using symbol as param_name that raise an error in params_for (#1121)

* fix using symbol as param_name that raise an error in params_for
* test added for param_name as symbol

kaminari-core/lib/kaminari/helpers/tags.rb

@@ -51,7 +51,7 @@ def page_url_for(page)
       private
 
       def params_for(page)
-        if (@param_name == :page) || !@param_name.include?('[')
+        if (@param_name == :page) || !@param_name.to_s.include?('[')
           page_val = !Kaminari.config.params_on_first_page && (page <= 1) ? nil : page
           @params[@param_name] = page_val
           @params

kaminari-core/test/helpers/tags_test.rb

@@ -81,6 +81,12 @@ class TagTest < ActionView::TestCase
           assert_match(/foo\.page=\d+/, Kaminari::Helpers::Tag.new(self, param_name: 'foo.page').page_url_for(2))
         end
       end
+
+      sub_test_case "with param_name = :symbol_param option" do
+        test 'using a symbol as param_name' do
+          assert_match(/symbol_param=\d+/, Kaminari::Helpers::Tag.new(self, param_name: :symbol_param).page_url_for(2))
+        end
+      end
     end
   end