Make bump from canary to master get all commits from latest master release

[timneutkens]

So what I run into with Next.js when merging canary into master is that release will only get the commits from the latest canary to the new master release.

For example:

1. I release Next.js 6.0.0
2. We started development on Next.js 6.0.1 with a canary release: 6.0.1-canary.0
3. We did some more commits
4. Releasing them as 6.0.0-canary.1. Commits from 6.0.1-canary.0 to 6.0.1-canary.1 are caught by release and added to the release notes
5. I finished the canary branch and it's ready to be released
6. I run release patch on the master branch with all commits from the canary branch
7. Release doesn't detect all commits from 6.0.0 to 6.0.1, making me have to manually copy-paste all release notes from canary releases.

@leo can we add support for this behaviour? It'd be a huge time saver for me when releasing 😌

[chabou]

Same problem with hyper.
And problem is even bigger when master and canary has diverged (using a cherry-pick strategy to merge canary into master). When you are releasing a first canary release after a stable release, it can't find last tag in canary branch and it seems to consider all commits from divergence.

This is due to this PR: #71
This is explicitly said that all branches are now valid to find previous tag which is good for hotfix/maintenance branch strategy. But not in our case.

Several simple ways to fix this:

• add an option to specify the previous tag manually. It will help to resolve all edge cases.
• add an option to strictly choose the previous tag of current branch.

More complicated solution that can come after:

• detect when previous tag is not on same branch, get previous tag on same branch and let user decide interactively which origin tag to choose: <previous_tag>, <previous_tag_on_same_branch> or specify manually.