elasticsearch: Add zlib to buildInputs for unfree

The unfree variant of elasticsearch uses autoPatchelfHook and since we
removed the dependency on file for the hook itself in
58a97dfb

 we no longer have zlib
propagated.

So we need to explicitly state that dependency here.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @apeschar, @basvandijk