Fix offenses from the new version of rubocop.

.rubocop.yml

@@ -118,6 +118,8 @@ Style/ClassVars:
 Style/PerlBackrefs:
   Enabled: false
 
+Style/TrivialAccessors:
+  AllowPredicates: true
+
 Style/WordArray:
   Enabled: false
-

lib/liquid/standardfilters.rb

@@ -42,7 +42,7 @@ module Liquid
     end
 
     def url_encode(input)
-      CGI.escape(input) rescue input
+      CGI.escape(input) unless input.nil?
     end
 
     def slice(input, offset, length = nil)