Travis refuses to build; sometimes. (Could not find update-config.json)

Im setting up Cucumber tests with Protractor using Travis but it refuses to build sometimes.

Got it running here:

https://travis-ci.org/Arquisoft/dechat_es1a/builds/514640663

But i reran the build and now it always fails:

https://travis-ci.org/Arquisoft/dechat_es1a/jobs/514666402

This is my travis.yml:

sudo: required
dist: trusty

language: node_js
node_js:
  - "stable"

before_install:
 - export CHROME_BIN=/usr/bin/google-chrome
 # start xvbfb for e2e tests with screen resolution 1280x1024x16
 - "export DISPLAY=:99.0"
 - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x16"
 # give xvfb some time to start
 - sleep 3
 - sudo apt-get update
 - sudo apt-get install -y libappindicator1 fonts-liberation
 - wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
 - sudo dpkg -i google-chrome*.deb
 - google-chrome --version


install:
  - npm install
  - node_modules/protractor/bin/webdriver-manager update

before_script:
 - npm start & 
script:
  - npm test

I really appreciate your help.