fix: don't merge array properties with custom opts (#616)

With a custom "headerCorrespondence" of two entries, commit message
subjects couldn't be parsed due to merge with the default (Angular).

For example, the following custom parser opts (ESLint style) wouldn't
work because "headerCorrespondence" is `['type', 'subject', 'subject']`
after the merge.

```js
{
  headerPattern: /^(.*):\s(.*)$/,
  headerCorrespondence: ['type', 'subject'],
}
```

Fixes #594

@commitlint/parse/src/index.js

@@ -1,12 +1,17 @@
 import {sync} from 'conventional-commits-parser';
 import defaultChangelogOpts from 'conventional-changelog-angular';
-import {merge} from 'lodash';
+import {isArray, mergeWith} from 'lodash';
 
 export default parse;
 
 async function parse(message, parser = sync, parserOpts = undefined) {
 	const defaultOpts = (await defaultChangelogOpts).parserOpts;
-	const parsed = parser(message, merge({}, defaultOpts, parserOpts));
+	const parsed = parser(
+		message,
+		mergeWith({}, defaultOpts, parserOpts, (objValue, srcValue) => {
+			if (isArray(objValue)) return srcValue;
+		})
+	);
 	parsed.raw = message;
 	return parsed;
 }

@commitlint/parse/src/index.test.js

@@ -98,6 +98,28 @@ test('uses custom opts parser', async t => {
 	t.deepEqual(actual, expected);
 });
 
+test('does not merge array properties with custom opts', async t => {
+	const message = 'type: subject';
+	const actual = await parse(message, undefined, {
+		headerPattern: /^(.*):\s(.*)$/,
+		headerCorrespondence: ['type', 'subject']
+	});
+	const expected = {
+		body: null,
+		footer: null,
+		header: 'type: subject',
+		mentions: [],
+		merge: null,
+		notes: [],
+		raw: 'type: subject',
+		references: [],
+		revert: null,
+		subject: 'subject',
+		type: 'type'
+	};
+	t.deepEqual(actual, expected);
+});
+
 test('supports scopes with /', async t => {
 	const message = 'type(some/scope): subject';
 	const actual = await parse(message);