fix: fall back to conventional commit-parser settings for missing keys

[marionebl]

Fixes #341, #399, #445

BREAKING CHANGE
This potentially changes implicit commitlint behaviour users may
have relied on in earlier versions. Instead of falling back to the
builtin commit-parser defaults we now default all keys to
conventional-changelog-angular.

[byCedric]

Are the defaultOpts and parserOpts deep objects? If not I can imagine that some users need to be informed when they define the property they have to fully define it. E.g.

const defaultOpts = { some: true, other: { abc: true, def: true } };
const parserOpts = { other: { abc: true } };

merge({}, defaultOpts, parserOpts) === {
    some: true,
    other: { abc: true },
};

I don't think we should use mergeDeep, can imagine that this is intended behaviour?

[escapedcat]

I am not sure about this topic so I approve the changes, but looking forward how this will end.

[marionebl]

Did a quick runkit notebook for this and I thing lodash.merge does deep merging (fortunately! :))

https://runkit.com/marionebl/5c00b3d947189a00134a944e

[prisis]

When is the release of this fix?

[byCedric]

@prisis see this comment. You can expect a new release somewhere around the first two weeks of 2019 😄

@escapedcat @marionebl Maybe it might be useful for others to prepare a milestone with a due date, so others can read about the next expected release date?