ci(Travis): Add --ignore-gpu-blacklist

Per plotly/plotly.js#1455

Author: thewtex

karma.conf.js

@@ -81,7 +81,7 @@ module.exports = function init(config) {
     customLaunchers: {
       ChromeHeadlessNoSandbox: {
         base: 'ChromeHeadless',
-        flags: ['--no-sandbox'],
+        flags: ['--no-sandbox', '--ignore-gpu-blacklist'],
       },
     },
     // browserNoActivityTimeout: 600000,