Using right object to set an attribute in the Document data type cons…

…tructor

I was confused with all the crap about inheritance in Lua... but now, I think
I know what I'm doing :)

couchdb.lua

@@ -52,7 +52,7 @@ function Document:new(schema)
  self.__index = self
  self.schema = schema
  if schema.id ~= nil then
- self.id = schema.id
+ o.id = schema.id
  end
  return o
 end