问grunt-exec在运行hexo时出现问题

EN

www/
    homepage_and_other_stuff/
    hexo_blog/
        hexo_stuff/
        package.json
        node_modules/
    node_modules/
    Gruntfile.js
    package.json

module.exports = function(grunt) {

    // Project config
    grunt.initConfig({
        pkg: grunt.file.readJSON("package.json"),

        // CLEAN and GENERATE the blog portion of the site
        exec: {
            cd_blog: "cd blog",
            clean_blog: "hexo clean",
            generate_blog: "hexo generate",
            go_back: "cd ../"
        }
    });

    // Tasks
    grunt.loadNpmTasks("grunt-exec");

    // Build
    grunt.registerTask("build", "Builds site for production", function() {
        grunt.log.writeln("Building site..."["blue"]);
        grunt.task.run("exec");
    });


};

Usage: hexo <command>
Commands: 
  help     Get help on a command. 
  init     Create a new Hexo folder.
  version  Display version information.
Global Options:
  --config  Specify config file instead of using _config.yml
  --cwd     Specify the CWD
  --debug   Display all verbose messages in the terminal
  --draft   Display draft posts
  --safe    Disable all plugins and scripts
  --silent  Hide output on console
For more help, you can use 'hexo help [command]' for the detailed information
or you can check the docs: http://hexo.io/docs/