Backport PR jupyter-server#886: Normalize os_path

Author: martinRenou

jupyter_server/utils.py

@@ -111,7 +111,7 @@ def to_os_path(path, root=""):
     parts = path.strip("/").split("/")
     parts = [p for p in parts if p != ""]  # remove duplicate splits
     path = os.path.join(root, *parts)
-    return path
+    return os.path.normpath(path)
 
 
 def to_api_path(os_path, root=""):