Update trader.coffee

Fixing variable names (just to be careful), this still need to be tested.
Also,
"
  updatePortfolio: (positions,platform,cb)->
    platform.getPositions positions,(err, result)=>
      if err?
        logger.error err
      else
        logger.verbose "updatePortfolio: #{inspect(result)}"
        for curr,amount of result
          @sandbox.portfolio.positions[curr] =
            amount:amount
        cb()
"
might need fix to include updating price? not sure about this