use __dirname

Bug: 1294413
Change-Id: I10fff9f43c9354e424d88f2a1eb47f9bc064f99b
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3439243
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Tim Van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Tim Van der Lippe <tvanderlippe@chromium.org>
diff --git a/scripts/devtools_paths.js b/scripts/devtools_paths.js
index 5581612..ca2cfcd 100644
--- a/scripts/devtools_paths.js
+++ b/scripts/devtools_paths.js
@@ -63,7 +63,7 @@
  * If it's standalone, it will be /path/to/devtools-frontend
  */
 function devtoolsRootPath() {
-  return path.dirname(path.dirname(__filename));
+  return path.dirname(__dirname);
 }
 
 /**