Loot entries serialise incorrectly

Note: All class, field and method names used are from the stable_29 MCP mappings.

Due to a typo in LootEntry.Serialiser#serialize(), instances of LootEntryTable have their type set to "item" when serialised, instead of "loot_table". Any produced loot table containing these entries will error when they are deserialised.

I have verified this in MCP 9.24(MC 1.9), MCP 9.28(MC 1.9.4), MCP 9.30(MC 1.10) and MCP 9.37(MC 1.11.2).

@unknown has verified this in snapshot 17w31b.

The cause of this issue is this if statement in LootEntry.Serialiser#serialize():

if (p_serialize_1_ instanceof LootEntryItem)
{
    jsonobject.addProperty("type", "item");
}
else if (p_serialize_1_ instanceof LootEntryTable)
{
    jsonobject.addProperty("type", "item");
}

The fix is to replace "item" with "loot_table".

This bug is only exposed if mods or other third-party applications are used to serialise loot tables, as vanilla does not serialise them.