v0.39.3

Fixes
 - `nvm install-latest-npm`: npm v6.14.18 can not be installed from npm < v4.4.4
 - ensure this variable is bound
 - `debug`: correct mistaken `-V` to `--version` from #2922
 - `debug`: `awk`: not an option: `--version` (#2922)
 - grep: warning: stray \ before / (#2919)
 - improve backward compatibility for non-gnu awk (#2917)
 - fix `nvm install` error `unknown condition: -ne` (#2915)

Tests
 - update test mocks (#2933)
 - move installation_node tests back to xenial
 - move tests that fail on focal to a separate suite that runs on xenial
 - update travis to use focal
 - [actions] fix `latest-npm` tests so they use this repo’s nvm instead of the last published one
 - fix nvm_list_aliases test to use mocks for LTS aliases

Docs
 - [meta] Improve contributors documentation (#2791)
 - [Docs] added WSL troubleshooting with solution to (6) Could not resolve host: raw.githubusercontent.com (#2961)

Refactors
 - add `nvm_wrap_with_color_code`; allow no color code