Attempt to fix .travis.yml

sh: 0: Can't open /etc/init.d/xvfb
SublimeText/UnitTesting#163

.travis.yml

@@ -8,6 +8,11 @@ env:
         # - UNITTESTING_TAG="master"
 
 
+# https://github.com/SublimeText/UnitTesting/issues/163
+services:
+  - xvfb
+
+
 # mutliple os matrix
 # https://docs.travis-ci.com/user/multi-os/#Python-example-(unsupported-languages)
 matrix:
@@ -75,12 +80,6 @@ before_install:
             python3 --version;
       fi
 
-    # enable gui, see https://docs.travis-ci.com/user/gui-and-headless-browsers
-    - if [ -z "$TOXENV" ] && [ "$TRAVIS_OS_NAME" == "linux"  ]; then
-            export DISPLAY=:99.0;
-            sh -e /etc/init.d/xvfb start;
-      fi
-
 
 install:
     - if ! [ -z "$TOXENV" ] && [ "$TRAVIS_OS_NAME" == "linux" ]; then