Update swampling.xml

Correcting item id's according to items.xml and wiki.
Update marsh stalker.xml

Correcting item id's according to items.xml. Fixing bug "Loot of a marsh stalker: 13 gold coins, an item of type 19740, a rope"
Merge pull request #1438 from triath/patch-5

Fix item id's in Marsh Stalker and Swampling