Add http protocol to profile website if none exists

This fixes a bug on the users' news page where an incorrect URL might be displayed.

Pullup's user news page (example: http://pullup.io/news/user/megamattron) pulls GitHub profile data to build the section in the top-right corner. If a user fills out their GitHub profile's URL field without a protocol (like http or https), this produces an incorrect link on Pullup.

This change adds the http:// protocol if none exists. Note that no permanent change is made, it's just in the display of the link at runtime. I believe this is how GitHub handles it, too.