Run grunt tasks from child directories

module.exports = function(grunt) {
    grunt.initConfig({
        concat: {
            options: {
                banner: '',
                separator: ';'
            },
            dist: {
                src: ["js/libs/script-1.js", "js/libs/script-2.js"],
                dest: 'js/libs/build.js'
            }
        },
        uglify: {
            makeUgly: {
                files: {
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            }
        }
      }
    });
	
	// load npm packages. 
	// Just go up however many directoires until you find your /node_modules/ folder. 
	// There is a setBase config option for Grunt but this way works for me.
    grunt.loadNpmTasks('../../../node_modules/grunt-contrib-uglify');
	grunt.loadNpmTasks('../../../node_modules/grunt-contrib-cssmin');

    // Default task(s).
    grunt.registerTask('default', ['concat', 'uglify']);
};