code: function createFromDependency(pluginName) {
      var npmID = PluginDependency.nameToNpmID(pluginName);
      var version = pkg.dependencies[npmID];
  
      return PluginDependency.create(pluginName, version);
  }
docs: Create a PluginDependency from a dependency of gitbook
  @param {String} pluginName
  @return {PluginDependency}