Flexbox grid columns not full width at small viewport sizes

Created by: dsozzi

Hi,

I noticed that using the flex grid, columns at small sizes don't fill the full width.

See: http://codepen.io/anon/pen/vKxQVx

set the grid to use flexbox and resize the window to small size. Notice how the columns don't fill the width. Shouldn't the columns have flex-grow: 1; ?

thanks