New dryer, old outlet
The manufacturer's installation instructions should contain a section on how to properly install a three prong cord on the dryer.  Buy a three prong cord, and follow the instructions to install it.  Keep the 4 prong cord, in case the next place has a 4 prong receptacle.

If you don't have the manufacturer's installation instructions for the dryer, you can usually download a copy from the manufacturer's website. You'll just need to know the model number to look it up.


  WARNING
  Using unlisted adapters found on the internet, or building ones yourself, is a good way to injure/kill someone.