[ci] update test script

* pin to defined distribution version
* fix required services
* fix wrong path to `ng`

.travis.yml

@@ -1,23 +1,21 @@
 language: node_js
-sudo: required
-node_js:
-   - node
-
-before_script:
-   - "sudo chown root /opt/google/chrome/chrome-sandbox"
-   - "sudo chmod 4755 /opt/google/chrome/chrome-sandbox"
+dist: bionic
 
-before_install:
-   - export CHROME_BIN=chromium-browser
-   - export DISPLAY=:99.0
-   - sh -e /etc/init.d/xvfb start
+services:
+   - xvfb # required for headless testing
 
-script: # the build step
-   - node_modules/.bin/ng test --watch=false
+node_js:
+   - lts/* # use lts version of node
 
+addons:
+   chrome: stable
 
 cache:
-  yarn: true
-  directories:
-     - ./node_modules
-     - ./.chrome/chromium
+   - npm
+
+install:
+   - npm set progress=false
+   - npm install
+
+script:
+   - ./node_modules/.bin/ng test --watch=false # run the test