fix #794

fix the issue that when a marshmallow old version (below 2.17.0) installed, an unexpected AttributeError raised cause there is no __version_info__ attribute in **__init__.py**.

Author: xzycn

hug/types.py

@@ -23,6 +23,7 @@
 
 import uuid as native_uuid
 from decimal import Decimal
+from distutils.version import LooseVersion
 
 import hug._empty as empty
 from hug import introspect
@@ -34,7 +35,7 @@
     import marshmallow
     from marshmallow import ValidationError
 
-    MARSHMALLOW_MAJOR_VERSION = marshmallow.__version_info__[0]
+    MARSHMALLOW_MAJOR_VERSION = getattr(marshmallow,'__version_info__',LooseVersion(marshmallow.__version__).version)[0]
 except ImportError:
     # Just define the error that is never raised so that Python does not complain.
     class ValidationError(Exception):