prompt undefined fix

Hello when i tried this grunt task i have this error blocking me :
Fatal error: Cannot read property 'prompt' of undefined
I had to patch out the script in order to have execution. 
After the patch i have outputs like this :
1=> "& did not start a character reference. (& probably should have been escaped as &amp;.)" Line no: undefined
(the typo was on the title tag in the html)
I don't know why this happened or if this patch could be useful to you but anyway i report it to you.
Thanks for your code.
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
prompt undefined fix

fix single quote & undefined
Merge pull request #54 from sylvaincombes/patch-1

prompt undefined fix