bindings/python: strip ~ from python version

Inspired by a suggestion of Xiyue Deng, this change ensures that
the python bindings have a version that recent setuptools is happy
with.

This will have the unfortunate side effect of the python view of the
version number differing from the rest of notmuch for the
pre-releases. The alternative would be to transform the version
numbers for the Debian packages for the pre-releases, as there is now
no version scheme that works for both, since setuptools started
rejecting versions with "~" in them.  If we decide to go the latter
way in the future, this change is easy to revert.

bindings/python-cffi/setup.py

@@ -2,7 +2,7 @@ import setuptools
 from _notmuch_config import *
 
 with open(NOTMUCH_VERSION_FILE) as fp:
-    VERSION = fp.read().strip()
+    VERSION = fp.read().strip().replace('~', '')
 
 setuptools.setup(
     name='notmuch2',