As of https://github.com/tc39/ecma262/commit/13906140a, the spec
now returns true when [[SetPrototypeOf]] is invoked with null
on a module namespace object.

R=neis@chromium.org
BUG=v8:1569

Review-Url: https://codereview.chromium.org/2557923004
Cr-Commit-Position: refs/heads/master@{#41575}