lang/nim: Update to 1.0.6

• Update to 1.0.6

Changelog:

• https://github.com/nim-lang/Nim/blob/version-1-0/changelogs/changelog_1_0_6.md

PR: 243760
Submitted by: Neal Nelson (maintainer)
Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D23770