Use date-based release numbers (python#11)

Author: Jon Wayne Parrott

setup.py

@@ -11,7 +11,9 @@
 
 setup(
     name='python-docs-theme',
-    version='0.0.1',
+    # Version is date based as year.month[.serial], where serial is used
+    # if multiple releases are needed to address build failures.
+    version='2018.2',
     description='The Sphinx theme for the CPython docs and related projects',
     long_description=long_description,
     author='PyPA',