fix travis config

.travis.yml

@@ -1,4 +1,17 @@
 language: node_js
+os: linux
+sudo: required
+dist: trusty
+addons:
+  apt:
+    packages:
+    - mesa-utils
+    - xvfb
+    - libgl1-mesa-dri
+    - libglapi-mesa
+    - libosmesa6
 node_js:
   - "10"
-  - "8"
+  - "8"
+before_script:
+  - export DISPLAY=:99.0; sh -e /etc/init.d/xvfb start