Add support for specifying release branch

[MunifTanjim]

Fixes: #466

Based on: #476

[sindresorhus]

If this option is not specified, I think we should allow main too, just to make it easier in this transitional phase.

[MunifTanjim]

If this option is not specified, I think we should allow main too, just to make it easier in this transitional phase.

So should we hardcode both master & main here?

np/source/git-util.js

Lines 41 to 45 in b4bef72

	exports.verifyCurrentBranchIsReleaseBranch = async (releaseBranch = 'master') => {
	if (await exports.currentBranch() !== releaseBranch) {
	throw new Error(`Not on \`${releaseBranch}\` branch. Use --any-branch to publish anyway, or set a different release branch using --branch.`);
	}
	};

Like this?

exports.verifyCurrentBranchIsReleaseBranch = async (releaseBranch) => {
	const allowedBranches = releaseBranch ? [releaseBranch] : ['master', 'main']
	const currentBranch = await exports.currentBranch()
	if (!allowedBranches.includes(currentBranch)) {
		throw new Error(`Not on ${allowedBranches.map(branch=> \`${branch}\`).join('/')} branch. Use --any-branch to publish anyway, or set a different release branch using --branch.`);
	}
};

[sindresorhus]

Correct