Advertise python 3.4 support and use that in Travis CI

We also don't need to update virtualenv, or use python3.5 specific
packages.

.travis.yml

@@ -9,9 +9,8 @@ git:
   depth: 1
 
 install:
-- sudo apt-get update
-- sudo apt-get install python3.5 python3.5-dev
-- sudo pip install --upgrade virtualenv
+  - sudo apt-get update
+  - sudo apt-get install python3 python3-dev
 
 script:
   - ./scripts/test-and-build.sh

README.rst

@@ -41,9 +41,9 @@ specs and event schemas in this repository.
 Preparation
 -----------
 
-To use the scripts, it is best to create a Python 3.5+ virtualenv as follows::
+To use the scripts, it is best to create a Python 3.4+ virtualenv as follows::
 
-  virtualenv env
+  virtualenv -p python3 env
   env/bin/pip install -r scripts/requirements.txt
 
 (Benjamin Synders has contributed a script for `Nix`_ users, which can be

scripts/test-and-build.sh

@@ -4,7 +4,7 @@ set -ex
 
 cd `dirname $0`/..
 
-virtualenv -p python3.5 env
+virtualenv -p python3 env
 . env/bin/activate
 
 # Print out the python versions for debugging purposes