http-server blocks the script on travis CI

Here is my .travis.yml:

language: node_js
node_js:
  - "node"
before_install:
  - npm install -g grunt-cli
  - npm install -g http-server
  - npm install -g bower
install:
  - npm install
  - bower install
services:
  - http-server
script: grunt mocha
after_success: "./travis.sh"   

I need the http-server to be listening to 8080 port when my grunt mocha task is running. But when travis CI job starts the server it just hangs the whole pipeline. On my local machine I start http-server in one console tab and grunt mocha in another. What is the workaround here?