add module docstring for versioning.py

stix2/patterns.py

@@ -1,4 +1,4 @@
-"""Classes to aid in working with the STIX 2 patterning language."""
+"""Classes to aid in working with the STIX2 patterning language."""
 
 import base64
 import binascii

stix2/versioning.py

@@ -1,3 +1,5 @@
+"""STIX2 core versioning methods."""
+
 import copy
 import datetime as dt
 import itertools