I am having an issue trying to get my Grunt.js file to work. Currently I have it set up to just concatenate all my php function files, and decided since a lot of my work projects use Bootstrap, to concatenate only the javascript files I'll be using. However, when I set it up, hoping I did set it up correctly, my grunt execution does not create/edit the javascript final destination file, nor the php functions file. I am not sure what I have done incorrectly but here is the following code:
module.exports = function (grunt) {
    // Project configuration.
    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),
        concat: {
            js: {
                options: {
                    separator: 'rn'
                },
                dist: {
                    src: [
                        // Comment or uncomment any Bootstrap JS files
                        // you will not be using
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/alert.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/button.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/carousel.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/collapse.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/dropdown.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/modal.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/phantom.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/popover.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/qunit.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/scrollspy.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/tether.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/tab.js',
                        'wp-content/themes/base_theme/assets/js/required/bootstrap/plugins/tooltip.js'
                    ],
                    dest: 'wp-content/themes/base_theme/assets/js/required/bootstrap/bootstrap.min.js'
                }
            },
            php: {
                options: {
                    stripBanners: true,
                    separator: '\n?>\n',
                },
                dist: {
                    src: [
                        // To create a new location, follow pattern below
                        // Comment out what you don't need a re-concat
                        'wp-content/themes/base_theme/assets/functions/basic.php',
                        'wp-content/themes/base_theme/inc/custom-header.php',
                        'wp-content/themes/base_theme/inc/customizer.php',
                        'wp-content/themes/base_theme/inc/extras.php',
                        'wp-content/themes/base_theme/inc/jetpack.php',
                        'wp-content/themes/base_theme/inc/template-tags.php',
                        'wp-content/themes/base_theme/inc/wpcom.php',
                        'wp-content/themes/base_theme/assets/functions/bootstrap-nav.php',
                        'wp-content/themes/base_theme/assets/functions/enqueue.php'
                        'wp-content/themes/base_themey/assets/functions/custom-post-type.php',
                        'wp-content/themes/base_theme/assets/functions/internal-template.php',
                        'wp-content/themes/base_theme/assets/functions/custom-taxonomy.php',
                        'wp-content/themes/base_theme/assets/functions/acf.php',
                        'wp-content/themes/base_theme/assets/functions/custom.php'
                        'wp-content/themes/base_theme/assets/functions/custom-sidebar.php'
                        ],
                    dest: 'wp-content/themes/base_theme/functions-mod.php'
                }
            }
        }
});
    // Load the plugins
    grunt.loadNpmTasks('grunt-contrib-concat');
    // Default task(s).
    grunt.registerTask('default', ['concat']);
};
My package.json is the following (I know I'm not using jshint or uglify as of yet in my grunt.js, I am just testing one at a time).
{
  "name": "base_theme",
  "version": "0.1.0",
  "devDependencies": {
    "grunt": "~0.4.5",
    "grunt-contrib-concat": "~1.0.0",
    "grunt-contrib-jshint":  "~0.8.0",
    "grunt-contrib-uglify":  "~0.2.7"
  }
}
I've tried reading through the documentation on grunt's website, but either I"m not understanding something correctly, or I am just doing something completely wrong