Update fbjni submodule to new upstream and latest version
Summary:
The central fbjni repository is now public, so point to it and
take the latest version, which includes support for host builds
and some condensed syntax.
Test Plan: CI
Differential Revision: D18217840
fbshipit-source-id: 454e3e081f7e3155704fed692506251c4018b2a1
