I'm going to assume you are using a Windows nightly build?
The deal is that the update to 2016.1.0 went in yesterday evening (Jan 5 19:44 UTC). The last Windows nightly looks like it built at Jan 5 01:14 UTC, so it will still be 3.7 but, as I write, it is currently building. If that build is successful, that should give you Flightgear 2016.1.0, including Simgear and dependencies.
http://build.flightgear.org:8080/job/Windows-nightly/It's possible that this build will fail, in which case you are stuck until someone fixes it.
Your best solution might be to go back to a 3.7 version of FGDATA, e.g. commit b640f6 and wait a few days until things stabilise with 2016.1.0.
EDIT: For anyone using nightly builds, don't pull FGDATA until you are able to get a nightly build from Jan 6 onwards.