grunt-contrib-uglifyでsourceMapのファイル名を可変にする方法 ref: http://qiita.com/panghea@github/items/b691b85e293b119a2f47

Gruntfile.js

    uglify: {
      options: {
          sourceMap: function(name) { return name.replace(/.js/,".map");} 
      },
      build: {
        files: [
                {
                  expand: true,
                  src: ['**/*.js'], 
                  dest: '../build/',
                  ext: '.js',  
                },
              ],
      }
    },