Support exclamation mark after type/scope of the "conventional commits" convention.

[jcornaz]

Acording to conventional commits the following commit message is valid and should be considered a "breaking change":

refactor!: drop support for Node 6

(example taken directly from the conventional commit spec: https://www.conventionalcommits.org/en/v1.0.0/#commit-message-with--to-draw-attention-to-breaking-change)

But it looks like clog ignores the commit messages that contain a ! after the type/scope.

I realized that the readme of this project points to the angular commit convention, rather than the conventional commits specification.

But would it be possible to consider the support of "conventional commit"?