test-module-loading: convert backslashes to forward slashes

This makes the test pass on Windows.

test/simple/test-module-loading.js

@@ -211,7 +211,8 @@ assert.deepEqual(json, {
 // the appropriate children, and so on.
 
 var children = module.children.reduce(function red(set, child) {
-  var id = path.relative(path.dirname(__dirname), child.id);
+  var id = path.relative(path.dirname(__dirname), child.id)
+  id = id.replace(/\\/g, '/');
   set[id] = child.children.reduce(red, {});
   return set;
 }, {});