Handle default branch properly

[cecton]

Hi,

Thank you for cargo-generate ❤️

I would like to introduce this change to make cargo-generate more friendly with repositories that don't use "master" as the default branch. I think this is particularly relevant now that GitHub also uses "main" instead of "master".

I would have like to fix it on cargo directly but there are some compatibility issues. But I don't think this is an issue for cargo-generate. This is why I'm introducing this change here.

I was personally bothered by it because I tried to make a new template but it failed because I was using the "main" branch as default branch.

[k0pernicus]

Hi @cecton, thanks for the update!

Everything is ok on my side - any comment(s) @sassman or I can merge it? :)

[sassman]

@k0pernicus unfortunately I cannot merge it, lacking the privileges. But looks good for me.

[k0pernicus]

Thanks again @cecton, and welcome as a contributor! :)

[cecton]

Thanks a lot! 🎉