Update sd6.svg

[ghost]

1. Removed the border in sd6.svg that popped up in the version submitted in Change the color of the icons on the Scientific Domains tab #479.
2. Fixed the cropped parts of the original icon.

[InessaPawson]

LGTM.

[MarsBarLee]

It looks great! I can see this time you've made a separate branch instead of pushing from the master branch, which is also great.

Next time I recommend you make your changes in your original PR, in this case #479. You can do that by making your changes in the same branch. When you do 'git push origin', the new commits will show up in the original PR page, which you can see if you scroll down the page see your PR commit history.

If you keep your commits in one PR, that makes it easier for us to review all your changes together.

For this case, I don't think you need to do that, we can separately accept each PR,#479 and #483.

[seberg]

Silly nitpick and invisible when scaled down, but the new version looks just slightly squeezed vertically to me? (Making the circles not round)

[ghost]

Will look into it @seberg