change master to main

[yibeichan]

Hi @djarecka,
I'm thinking of changing master here to main since the default branch in a new github repo now is main. So if other people clone or fork this demo, they don't have to do the change manually.

demo-protocol/.github/workflows/build_deploy.yml

Lines 11 to 13 in 16a54ef

	branches: [ master ]
	pull_request:
	branches: [ master ]

demo-protocol/.github/workflows/build_deploy.yml

Line 68 in 16a54ef

if: github.ref == 'refs/heads/master'

If you agree, I'll change the default branch in this repo to main and then update the above yml file accordingly.