Update .travis.yml

.travis.yml

@@ -5,12 +5,6 @@
 language: c
 sudo: false
 
-addons:
-  apt:
-    packages:
-    # for testing racket/gui/base
-    - libgtk-3-dev
-
 env:
   global:
     - RACKET_DIR=~/racket
@@ -35,6 +29,8 @@ matrix:
   fast_finish: true
 
 before_install:
+  - "export DISPLAY=:99.0"
+  - "sh -e /etc/init.d/xvfb start"
   - git clone https://github.com/mbutterick/travis-racket.git
   - cat travis-racket/install-racket.sh | bash # pipe to bash not sh!
   - export PATH="${RACKET_DIR}/bin:${PATH}" #install-racket.sh can't set for us