No merge commit on finishFeature with isRebase set to true

[JTBrinkmann]

when finishing a feature with the isRebase option set to true, the develop branch is fast-forwarded instead of being merged. Expected behavior (imo) is that the isRebase flag causes a rebase on develop before (additionally) merging with a forced merge-commit.

Gitflow explicitly specifies forcing a merge commit (--no-ff), so I whould consider this a nodegit-flow bug.

nodegit-flow/src/Feature.js

Lines 119 to 122 in fdf742b

	// If the develop branch and feautre branch point to the same thing do not merge them
	// or if the `isRebase` parameter is true do not merge
	const isSameCommit = developCommit.id().toString() === featureCommit.id().toString();
	cancelDevelopMerge = isSameCommit || isRebase;