duplication of output file

[neilhanvey]

whenever i run my grunt file it creates a duplicate of my output css file in my source directory. my grunt file is below. the weird thing is that i've got source map turned off for output but this duplicate created in my source folder has a source map. version of sass i'm using is the latest (selective steve)

module.exports = function (grunt) {
// load Grunt plugins from NPM
grunt.loadNpmTasks('grunt-contrib-uglify');
grunt.loadNpmTasks('grunt-contrib-watch');
grunt.loadNpmTasks('grunt-contrib-sass');

// configure plugins
grunt.initConfig({
    watch: {
        styles: {
            files: ['Content/**/*.scss'],
            tasks: ['sass']
        },
        options: {
            livereload: true
        }
    },
    sass: {                              
        dev: {                            
            options: {                    
                style: 'compact',
                sourcemap: 'none'
                },
            files: [{
                expand: true,
                cwd: 'Content/lib/materialize-src/sass',
                src: ['*.scss'],
                dest: 'Content/css',
                ext: '.css'
            }]
        }
    }
});

// define tasks
grunt.registerTask('server', ['watch']);

};