Fix header typo in rapidjson. Was found when using the custom test harness. Bug: angleproject:3162 Change-Id: I9db11eddb51508ff1eaebe02c106cd4a95c369b1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1932342 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>