gplugin/gplugin

Fix the build when ran in a meson subproject.
feature/meson-subproject-fix
2019-08-12, Gary Kramlich
923cbd2a8055
Fix the build when ran in a meson subproject.

We were using meson.build_root() when we should have been using
meson.current_build_dir().
export GPLUGIN_VERSION=@GPLUGIN_MAJOR_VERSION@.@GPLUGIN_MINOR_VERSION@.@GPLUGIN_MICRO_VERSION@