Disabled CI for Python <3.5 due to incompatibility with required dependencies.

Signed-off-by: Maciej Kurc <mkurc@antmicro.com>

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index c5e4270..c9d1b5e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,8 +1,6 @@
 language: python
 
 python:
-  - 2.7
-  - 3.4
   - 3.5
   - 3.6
   - 3.7