bug fix to only get USD
Added a check for USD when canceling existing orders.
Changed the minimum amount to lend to $100. This was confirmed with Bitfinex support.
Changed the minimum amount back to $50. The $50 is what the min is as reported back from the API & it works.
Merge pull request #4 from Scottiiee/master

Bug fixes:
Only cancel USD swap offers when changing the offered rate and amount.