Make dateutil pin a post-release version

Adds a post-release segment to force the fixed mediatimestamp to replace
the original one in pip's caches.

Author: samdbmg

setup.py

@@ -18,7 +18,7 @@
 
 # Basic metadata
 name = 'mediatimestamp'
-version = '1.7.0'
+version = '1.7.0.post0'
 description = 'A timestamp library for high precision nanosecond timestamps'
 url = 'https://github.com/bbc/rd-apmm-python-lib-mediatimestamp'
 author = 'James P. Weaver'