Enable Style/DefWithParentheses cop and fix single offense

.rubocop.yml

@@ -152,7 +152,7 @@ Style/ConstantName:
 
 # Use def with parentheses when there are arguments.
 Style/DefWithParentheses:
-  Enabled: false
+  Enabled: true
 
 # Checks for use of deprecated Hash methods.
 Style/DeprecatedHashMethods:

lib/api/helpers.rb

@@ -29,7 +29,7 @@ module API
       @current_user
     end
 
-    def sudo_identifier()
+    def sudo_identifier
       identifier ||= params[SUDO_PARAM] || env[SUDO_HEADER]
 
       # Regex for integers