fix(top-level): support git submodules (#784)

* fix: modify the parameters for the sander.readFile function (#448)

* fix: modify the parameters for the sander.readFile function (#448) - prettier lint fix

* fix: do NOT specify the .git to be a directory in case of the git submodule not able to work properly

* fix: add a new function 'searchDotGit' to make sure we can find a correct .git path which can be file or directory (#784)

Author: huanghai21

@commitlint/top-level/src/index.ts

@@ -14,11 +14,21 @@ export default toplevel;
  * Find the next git root
  */
 async function toplevel(cwd: string) {
-	const found = await up('.git', {cwd, type: 'directory'});
+	const found = await searchDotGit(cwd);
 
 	if (typeof found !== 'string') {
 		return found;
 	}
 
 	return path.join(found, '..');
 }
+
+/**
+ * Search .git, the '.git' can be a file(submodule), also can be a directory(normal)
+ */
+async function searchDotGit(cwd: string) {
+	const foundFile = await up('.git', {cwd, type: 'file'});
+	const foundDir = await up('.git', {cwd, type: 'directory'});
+
+	return foundFile || foundDir;
+}