Update CONTRIBUTING.md

PocketMine namespaces are all in lowercase letters.
Merge pull request #1859 from PEMapModder/patch-2

Update CONTRIBUTING.md
Fixed #1826 Block damage values were swapped in McRegion
Merge branch 'master' of github.com:PocketMine/PocketMine-MP
Possible fix for 'Invalid Chunk given' crash
Players are now moved using the head, closes #1842
Fixed source servers getting invalid AutoUpdater notifications
Made AsyncTask::onCompletion() implementation optional
Fixed RCON usage
Remove head offset from client-side MovePlayerPacket
Implemented circular chunk sending
Level formats can send chunks without creating an AsyncTask, API 1.2.1 (small fix, no changes)
Fixed AddMobPacket's Type - (is now int)

Thanks @Intyre!
Merge pull request #1875 from KnownUnown/patch-1

Fixed AddMobPacket's Type - (is now int)
Fixed chunk sending
Order chunks to be generated
Added Exception handling on level loading
Improved chunk cache, clean invalid chunks
Move players from eye level, not top of head
Send player movements as direct packets