Travis give error but compiles on pc

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Javascript

Node.js

I'm making a web server with Node.JS and use Travis-Ci to check my code. Yhe problem I got is when I commit my code, Travis gives error below, but the code compiles without an error on my pc:

./backend/server.js: 1: Syntax error: ( unexpected

Here you could find my `.travis.yml` file:

install:
  - npm install
  - npm install -g bower
  - bower install bootstrap
  - bower install socket.io
language: node_js
node_js:
  - "6.9"
before_script: 
  - chmod 0777 ./backend/server.js
cache:
  directories:
    - node_modules
    - bower_components

and the `package.json`

{
  "name": "watchfriends",
  "version": "0.0.0",
  "description": "Front-end and back-end project watchfriends",
  "main": "gulpfile.js",
  "scripts": {
    "test": "./backend/server.js"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/WatchFriends/Backend.git"
  },
  "author": "Hein P., Jasper D., Michiel V., Michiel Z.",
  "license": "ISC",
  "bugs": {
    "url": "https://github.com/WatchFriends/Backend/issues"
  },
  "homepage": "https://github.com/WatchFriends/Backend#readme",
  "devDependencies": {
    "gulp": "^3.9.1",
    "gulp-autoprefixer": "^3.1.1",
    "gulp-clean-css": "^2.0.13",
    "gulp-concat": "^2.6.1",
    "gulp-csslint": "^1.0.0",
    "gulp-htmlhint": "^0.3.1",
    "gulp-jshint": "^2.0.4",
    "gulp-notify": "^2.2.0",
    "gulp-sass": "^2.3.2",
    "gulp-sourcemaps": "^2.2.0",
    "gulp-uglify": "^2.0.0",
    "jshint-stylish": "^2.2.1"
  },
  "dependencies": {
    "socket.io": "^1.5.1"
  }
}

On this gist, you could find my code, including the log.

Did I something wrong?

Thanks in advance.

What I have tried:

I've tried to Google it but nothing found.