Explicitly include test/ in release tarballs. Closes GH-1384.

progval · progval · commit 103210e6835c · 2019-10-28T18:17:13.000+01:00
distutils whitelists 'test/test*.py', which unfortunately excludes
'test/__init__.py', which is needed by supybot-test.
diff --git a/MANIFEST.in b/MANIFEST.in
@@ -3,3 +3,4 @@ include README.md
 include Makefile
 include .travis.yml
 include requirements.txt
+include test/*.py
