Drop Python 3.4 support for now

The asyncore module included with Python 3.4 has regressed and since
even Debian stable is shipping Python 3.5 now, I don't see a reason to
keep support around anymore.

Upstream bug: https://bugs.python.org/issue13103

.travis.yml

@@ -2,7 +2,6 @@ language: python
 sudo: false
 cache: pip
 python:
-- 3.4
 - 3.5
 - 3.6
 install: