Add contrib-clean to Grunt.

We should clean 'min' directory before build.

Gruntfile.js

@@ -10,6 +10,9 @@ module.exports = function (grunt) {
       '<%= pkg.homepage ? "* " + pkg.homepage + "\\n" : "" %>' +
       '* Copyright (c) <%= grunt.template.today("yyyy") %> <%= pkg.author.name %>;' +
       ' Licensed <%= _.pluck(pkg.licenses, "type").join(", ") %> */\n',
+    clean: {
+      files: ['min']
+    },
     // Task configuration.
     uglify: {
       options: {
@@ -65,6 +68,7 @@ module.exports = function (grunt) {
   // These plugins provide necessary tasks.
   grunt.loadNpmTasks('grunt-contrib-uglify');
   grunt.loadNpmTasks('grunt-contrib-jshint');
+  grunt.loadNpmTasks('grunt-contrib-clean');
   grunt.loadNpmTasks('grunt-contrib-csslint');
   grunt.loadNpmTasks('grunt-contrib-cssmin');
 
@@ -76,6 +80,6 @@ module.exports = function (grunt) {
   });
 
   grunt.registerTask('lint', ['jshint', 'csslint']);
-  grunt.registerTask('build', ['uglify', 'cssmin']);
+  grunt.registerTask('build', ['clean', 'uglify', 'cssmin']);
 
 };

package.json

@@ -9,6 +9,7 @@
     "grunt-contrib-jshint": "~0.1.1",
     "grunt-contrib-uglify": "~0.1.1",
     "grunt-contrib-cssmin": "~0.6.1",
-    "grunt-contrib-csslint": "~0.1.2"
+    "grunt-contrib-csslint": "~0.1.2",
+    "grunt-contrib-clean": "~0.4.1"
   }
 }