(cron) fix validation thanks @alisamar, closes https://github.com/opnsense/core/issues/769

(cherry picked from commit d92af436)

src/opnsense/mvc/app/models/OPNsense/Cron/Cron.xml

@@ -24,7 +24,7 @@
                 <hours type="TextField">
                     <default>0</default>
                     <Required>Y</Required>
-                    <mask>/^((?:\*|[1-2][0-3]|0[0-9]|[0-9])(,{1}|-{1}|$))+$/</mask>
+                    <mask>/^((?:\*|([1][0-9]|[2][0-3])|0[0-9]|[0-9])(,{1}|-{1}|$))+$/</mask>
                     <ValidationMessage>Value needs to be between 0 and 23, multiple values, ranges and * are supported (ex. 1,2,8 or 0-8 )</ValidationMessage>
                 </hours>
                 <days type="TextField">