Add cache, disable faulthandler

.travis.yml

@@ -1,17 +1,19 @@
+os: linux
 dist: xenial
 services:
   - xvfb
 language: python
+cache: bundler
 sudo: required
 addons:
   apt:
     packages:
       - libenchant-dev
 python:
-  - "3.5"
+  - "3.7"
 install:
   - pip install -r requirements.txt
-  - pip install pytest-faulthandler
+# - pip install pytest-faulthandler
   - pip install pytest-cov
   - pip install pytest-qt
   - pip install codecov