Requires.io uses badges generated by shields.io. Today (February 1st, 2015) shields.io is switching its default badges to a sleek, flat design. The rational is that it will be a better match for GitHub overall design.
For consistency purpose, we have decided to make the switch:
You can of course still use the former style (called "plastic") by appending a GET parameter to badges requests, like this: &style=plastic.