The original headline is "Londoners Could Elect City's First Muslim Mayor" If you're going to change it, may I suggest "its" not it's" as in http://grammarist.com/spelling/its-its/
(edit I see that's the verbatim subheading of the original article. Still not a great choice)
Sadiq Khan (Labour) is leading in the polls, with Zac Goldsmith (Conservative) running second.