Some truecolour colourschemes in `help colors` don't actually work

[thesketh]

Hey, I've just discovered micro (long time nano user) and I really like it, thanks for working on this. The ease of installation is a godsend - no longer do I have to compile new versions of nano on our HPC cluster!

I noticed some mistakes in in > help colors

Description of the problem or steps to reproduce

1. Try to set colour scheme to atom-dark-tc or github-tc using > set colorscheme
2. Get error message about non-existent colour scheme

atom-dark (without the -tc suffix) works, but github doesn't.

$COLORTERM is set to truecolor, $MICRO_TRUECOLOR is set to 1.

Specifications

Commit hash: c51f849
OS: Linux (Ubuntu Budgie 18.04)
Terminal: Tillix

[SanchithHegde]

I noticed the same and figured out that the color schemes no longer exist in the runtime/colorschemes directory. It seems that there was already a PR open (#1588) to update the doc.