Updated travis.yml to allow GUI tests

.travis.yml

@@ -3,6 +3,10 @@
 language: python
 python: 2.7
 
+before_install:
+  - "export DISPLAY=:99.0"
+  - "sh -e /etc/init.d/xvfb start"
+
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 install:
   - pip install Scrapy docopt
@@ -16,4 +20,4 @@ notifications:
   slack: descartes2:6sgCzx3PvrO9IIMwKxj12dDM
 
 after_success:
-  coveralls --verbose
+  coveralls --verbose