Changed typo '.clear' to '.clearfix' in utility-classes.html

Seems to be a typo here, not 100% up to date on Foundation 5, but a quick Chrome Dev Tools test showed that .clear did not clear the floats inside the element, but .clearfix did
Merge pull request #3585 from fusion2004/patch-1

Changed typo '.clear' to '.clearfix' in utility-classes.html