Replace reject_blocked with reject_blocked! in callbacks.

In Rails 4.2 and below, skipping callbacks (skip_before_action, skip_after_action, etc.) that use methods which do not exist will not throw any errors.

On the other hand, Rails 5 does. See https://github.com/rails/rails/pull/19029

After testing with Rails 5 I noticed there are some methods that don't actually exist (because they were renamed, usually), this fixes a few instances of those.

reject_blocked! was introduced in c9def945, I can't find any references to reject_blocked ever existing.

app/controllers/explore/application_controller.rb

 class Explore::ApplicationController < ApplicationController
-  skip_before_action :authenticate_user!, :reject_blocked
+  skip_before_action :authenticate_user!, :reject_blocked!
 
   layout 'explore'
 end

app/controllers/help_controller.rb

 class HelpController < ApplicationController
-  skip_before_action :authenticate_user!, :reject_blocked
+  skip_before_action :authenticate_user!, :reject_blocked!
 
   layout 'help'
 

app/controllers/search_controller.rb

 class SearchController < ApplicationController
-  skip_before_action :authenticate_user!, :reject_blocked
+  skip_before_action :authenticate_user!, :reject_blocked!
 
   include SearchHelper