grunt watch command does nothing in terminal

I'm very new to programming and am trying to teach myself HTML and CSS3 so I apologize in advance if I don't make sense or if I don't understand what it is that's wrong with my code. The problem is that when I type in grunt watch into the terminal command line nothing happens. I've been trying to use autoprefixer(https://github.com/postcss/autoprefixer) and grunt. I followed this websites (http://css-tricks.com/autoprefixer/) instructions; however, I tried to modify the code for the grunt file slightly so that it would provide prefixes for any browser that has a market share higher than 1%.

Here is my altered gruntfile.js code.

module.exports = function (grunt) {
    grunt.initConfig({
        autoprefixer: {
            options: {
                browsers: ['>1%']
            }
            dist: {
                files: {
                    'build/style.css': 'style.css'
                }
            }
        },
        watch: {
            styles: {
                files: ['style.css'],
                tasks: ['autoprefixer']
            }
        }
    });
    grunt.loadNpmTasks('grunt-autoprefixer');
    grunt.loadNpmTasks('grunt-contrib-watch');
};

and here is my package.json file

{
    "name": "grunt-autoprefixer",
    "version": "0.1.1",
    "description": "Parse CSS and add vendor-prefixed CSS properties using the Can I Use database. Based on Autoprefixer.",
    "devDependencies":{
        "grunt": "~0.4.4",
        "grunt-contrib-watch" : "0.6.1",
        "grunt-autoprefixer" :"latest"
    }
}

I know it's very similar to this question (Node.js/Grunt - Can't run Grunt's watch - why?) but the author of the question didn't state what he changed to make it work in the end. Thanks