Should be imperative mood, there is no such thing as imperative tense

[mcrosby114]

https://github.com/commitizen/cz-conventional-changelog/blob/d4bf98e59b0d24e18876945546181ada5e2f7448/engine.js#L64

Just a nitpick, but it would be an improvement to re-word this message, perhaps with a brief example in the line. At the very least, this should be replaced with "mood" instead of "tense". I like how this example explains the intent of this type of commit message (https://git.kernel.org/pub/scm/git/git.git/tree/Documentation/SubmittingPatches):

Describe your changes in imperative mood, e.g. "make xyzzy do frotz" instead of "[This patch] makes xyzzy do frotz" or "[I] changed xyzzy to do frotz", as if you are giving orders to the codebase to change its behavior. Try to make sure your explanation can be understood without external resources. Instead of giving a URL to a mailing list archive, summarize the relevant points of the discussion.

[jimthedev]

That'd be wonderful. Care to venture a PR?