Add guard for nil

Author: Travers McInerney

lib/zendesk_apps_support/validations/source.rb

@@ -42,7 +42,8 @@ def jshint_error(file)
 
         def jshint_errors(files)
           files.each_with_object([]) do |file, errors|
-            errors << jshint_error(file)
+            error = jshint_error(file)
+            errors << error unless error.nil?
           end
         end