CI: switch to chrome-headless on Travis (#221)

Author: holgerd77

.travis.yml

@@ -5,14 +5,12 @@ node_js:
   - "11"
   - "12"
 addons:
-  firefox: "latest"
+  chrome: stable
   apt:
     sources:
     - ubuntu-toolchain-r-test
     packages:
     - g++-4.8
-before_install:
-  - sh -e /etc/init.d/xvfb start
 env:
   global:
     - DISPLAY=:99.0

karma.conf.js

@@ -37,9 +37,6 @@ module.exports = function (config) {
       enabled: true,
       usePhantomJS: false,
       postDetection: function (availableBrowser) {
-        if (process.env.TRAVIS) {
-          return ['Firefox']
-        }
         if (availableBrowser.includes('Chrome')) {
           return ['ChromeHeadless']
         }