Remove python 3.4 from build matrix

This is a very old version of python that almost nobody uses. There's
little value on maintaining it, and some of our dependencies started
dropping support for it, so let's simply forget about it and remove it
from our build matrix.

Signed-off-by: Rodrigo Tobar <rtobar@icrar.org>

.travis.yml

@@ -38,7 +38,6 @@ matrix:
     - python: "3.7"
     - python: "3.6"
     - python: "3.5"
-    - python: "3.4"
     - python: "2.7"
 
 # We want to use docker during the tests