Fix magnesium color bug

[PlethoraChutney]

The color-by-element node was mis-wired between atomic numbers 14 and 15. This resolves #254.

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (4e8225d) 53.73% compared to head (f012450) 53.73%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #264   +/-   ##
=======================================
  Coverage   53.73%   53.73%           
=======================================
  Files          15       15           
  Lines        1952     1952           
=======================================
  Hits         1049     1049           
  Misses        903      903           

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[BradyAJohnston]

Fabulous! I still haven't come up with a good way of actually versioning the hand-made nodes via git (.blend files are opaque to it) so I think we basically have to rely upon using tests to ensure that things don't change majorly when people edit the files.