Fix exception derp.

Author: brndnmtthws

optimal-buy-gdax.py

@@ -145,7 +145,7 @@ def get_prices():
         ticker = gdax_client.get_product_ticker(
             product_id='{}-{}'.format(c, args.fiat_currency))
         if 'price' not in ticker:
-            raise('no price available for {} ticker={}'.format(c, ticker))
+            raise(Exception('no price available for {} ticker={}'.format(c, ticker)))
         print('{} ticker={}'.format(c, ticker))
         prices[c] = float(ticker['price'])
     return prices