fixup! fixup! fixup! fixup! path: fix posix.relative() on Windows

Author: Trott

test/parallel/test-path-resolve.js

@@ -13,7 +13,7 @@ const posixyCwd = common.isWindows ?
   (() => {
     const _ = process.cwd()
       .replaceAll(path.sep, path.posix.sep);
-    return _.substr(_.indexOf(path.posix.sep));
+    return _.slice(_.indexOf(path.posix.sep));
   })() :
   process.cwd();