Update lib/github/tree.js

Co-authored-by: Antoine du Hamel <duhamelantoine1995@gmail.com>

lib/github/tree.js

@@ -42,7 +42,7 @@ export default class GitHubTree {
         `Cannot find WPT for "${path}". Please check the WPT name.`,
         this.cli.SPINNER_STATUS.FAILED
       );
-      process.exit();
+      throw new Error('Cannot find last commit');
     }
     return targetHistoryNodes[0].oid;
   }