Fix jumbotron padding

Created by: bangzek

Please do visual comparison between: http://getbootstrap.com/docs/4.0/examples/narrow-jumbotron/ and: https://getbootstrap.com/docs/3.3/examples/jumbotron-narrow/

You would find v4 jumbotron padding is so much longer on the vertical.

On the old v3 the space is 68px on the vertical and 60px on horizontal, this is because h1 has 20px margin-top.

In the current v4 the vertical is 64px (on normal 16px default font size) and 32px on horizontal. Probably v4 just copy the older padding proportion but failed to adjust with the removal of all margin-top.

I propose to just make the padding equal, so the end result will be 64px on both.

BTW, the example thumbnails needs updating.