Add prompt for breaking changes

[hassankhan]

Description

What is the use case that should be solved?

We should have the prompts ask if a breaking change is being committed. If true, then we should prepend the commit body with BREAKING CHANGE:.

For example:

feat(foo): Add new foo

BREAKING CHANGE: API has now changed

Version of cz-github you're using: 1.0.5

Node Version: 8.11

Operating System: macOS 10.13