display dense to avoid holes in the grid

[ymulenll]

hey @codediodeio, you could probably include grid-auto-flow: dense; to avoid having holes in the gallery, for example if you remove the first 3 images you can see something like this: http://recordit.co/NETNEk6Fix

but using grid-auto-flow: dense;: http://recordit.co/2eIfqBBjNV

(even though if it's not the best for accessibility because of the changes in the order of the cards) Thanks for your great content!