Replaced clearfix content property period with a space to prevent layout...

# Clearfix content period fix

Using a period for the content property in a clearfix can break layouts. See: http://perishablepress.com/lessons-learned-concerning-the-clearfix-css-hack/

Ted and Tony noticed your awesome grid generator was using the period when they were showcasing it to new FEDs in a workshop. I thought I would submit this PR while it was fresh on my mind.

I love the generator!