fix CoinbaseError init

Author: chris-martin

coinbase/models/error.py

@@ -4,4 +4,4 @@
 class CoinbaseError(Exception):
 
     def __init__(self, message, errors=None):
-        super(CoinbaseError, Exception).__init__(self, ' '.join([message] + (errors or [])))
+        super(CoinbaseError, self).__init__(self, ' '.join([message] + (errors or [])))

coinbase/tests/test_error.py

@@ -0,0 +1,6 @@
+from coinbase.models import CoinbaseError
+
+
+def test_coinbase_error_instantiation():
+    CoinbaseError("message")
+    CoinbaseError("message", ["abc", "def"])