fix LIBRARY_PATH for ubuntu xenial lmdb 0.9.17
fix LIBRARY_PATH for ubuntu xenial lmdb 0.9.17

xenial doesn't ship a .pc for lmdb and has it in an elaborate lib/ path:
/usr/lib/x86_64-linux-gnu/

Drup/ocaml-lmdb,Drup/ocaml-lmdb