The original repository for the npre-external-master repository was
removed and was re-uploaded [1]. This changed the commit hash for the
build.lock. This patch updates the commit hash to point to the head of
the new repository main branch as it hasn't changed since 2017.
[1] - https://github.com/juju/layer-index/pull/120
Change-Id: I000ee613a3739da6e218701e1e47a230dca3a8e3