fix: use grouped regex to ignore merge commits (#439)

Author: byCedric

@commitlint/is-ignored/src/index.js

@@ -3,7 +3,7 @@ import semver from 'semver';
 const WILDCARDS = [
 	c =>
 		c.match(
-			/^(Merge pull request)|(Merge (.*?) into (.*?)|(Merge branch (.*?))(?:\r?\n)*$)/
+			/^((Merge pull request)|(Merge (.*?) into (.*?)|(Merge branch (.*?)))(?:\r?\n)*$)/
 		),
 	c => c.match(/^(R|r)evert (.*)/),
 	c => c.match(/^(fixup|squash)!/),

@commitlint/is-ignored/src/index.test.js

@@ -107,3 +107,7 @@ test('should return true for bitbucket merge commits', t => {
 test('should return true for automatic merge commits', t => {
 	t.true(isIgnored('Auto-merged develop into master'));
 });
+
+test('should return false for commits containing, but not starting, with merge branch', t => {
+	t.false(isIgnored('foo bar Merge branch xxx'));
+});