Fix no attribute error printing ApiException

Fixes #177

Signed-off-by: jesus m. rodriguez <jmrodri@gmail.com>

Author: jmrodri

docusign_esign/client/api_exception.py

@@ -29,6 +29,9 @@ def __init__(self, status=None, reason=None, http_resp=None):
             self.reason = reason
             self.body = None
             self.headers = None
+            self.trace_token = None
+            self.timestamp = None
+            self.response = None
 
     def __str__(self):
         """