Merge pull request p12tic#104 from p12tic/fix-ci

travis: Update python version for tests

.travis.yml

@@ -1,14 +1,14 @@
 # Travis CI configuration file
 # http://about.travis-ci.org/docs/
-dist: trusty
+dist: bionic
 
 language: python
 
 # Available Python versions:
 # http://about.travis-ci.org/docs/user/ci-environment/#Python-VM-images
 python:
-  - "3.5"
   - "3.6"
+  - "3.7"
 
 # Dependencies installation commands
 install: