Added compatibility for CraftBukkit/Spigot 1.10.
Please note: At the time of posting this there is a bug in 1.10 that makes armor stands fall through the world if you summon one with no gravity and then turn on it's gravity.
I have reported the bug and I expect it should be fixed quickly.
Edit: The bug is now fixed. If you have this problem, run buildtools to update your CB/Spigot.