rename "master" to "main"

[lheagy]

Similar to simpeg/simpeg#980, we will update the name of our main branch to "main" in our geosci repos

• [x] geosci-labs
• [x] gpg
• [x] gpgLabs
• [x] em
• [x] website (including courses, disc, etc)
• [x] toolkit

to get these changes locally, you will need to run

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a

[lheagy]

👋 @yangdikun, I will let you update the

• [ ] ess302website repo

if you like. It is quite straightforward: https://github.com/github/renaming Feel free to ping if you have any questions!