Gulp command opens gulp.js in notepad instead of running it

I did install it correctly i think.

My package.json

   {
      "name": "my-project",
      "version": "0.1.0",
      "devDependencies": {
        "gulp": "^3.8.11",
        "gulp-concat": "^2.5.2"
      }
    }

my gulp.js

var gulp = require('gulp');

    var concat = require('gulp-concat');

    gulp.task('scripts', function() {
        return gulp.src('js/*.js')
          .pipe(concat('main.js'))
          .pipe(gulp.dest('build/js'));
    });

    gulp.task('default', ['scripts']);

my folder are as follow :

ROOT/package.json
ROOT/gulp.js
ROOT/node-modules/   <-- my modules are here
ROOT/js/  <-- my js are here

When I run gulp in command line, being in the ROOT folder, gulp.js just opens in windows notepad and thats all..

Why is it doing that ?

Also this might be terribly stupid from me but I'm not actually running a local server. I dont have wamp installed on this computer. Just figured it might be a problem for node.js