Add xvfb and pytest-xvfb packages

.travis.yml

@@ -15,7 +15,11 @@ python:
   - "pypy"
   - "pypy3"
 
-addons: {apt: {packages: [xsel]}}
+addons:
+  apt:
+    packages:
+      - xvfb
+      - xsel
 
 deploy:
   true:
@@ -28,14 +32,8 @@ deploy:
   password:
     secure: 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
 
-
-before_script:
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
-  - sleep 3 # give xvfb some time to start
-
 install:
-  - pip install cryptography pytest pytest-cov six mock coveralls --upgrade
+  - pip install cryptography pytest pytest-cov pytest-xvfb six mock coveralls --upgrade
   - python setup.py install
 
 script: