Make neo4j 1.9.M05 the minimum version

Not sure if this applies for the community version of neo4j.rb. But neo4j.rb 2.2.4 is incompatible with neo4j 1.8.2 (HA doesn't work). So I'm adding a 1.9.M05 constraint here in the hopes it saves somebody else from figuring this out on his own.

Perhaps there's a better place to do this, though, because community 1.8.2 might work with 2.2.4.