prompt undefined fix

Better patch of the "bug". To reproduce it put a jekyll like page in a html page, (exemple file begin with a '-' character). The task fail with 'prompt undefined', with the patch the output change to :
Validation started for.. web/jekyll.html
1=> "character \"-\" not allowed in prolog" Line no: 1
2=> "end of document in prolog" Line no: 5
No of errors: 2