npm install 过程中怎么会调用 grunt，有点奇怪啊，为何会这样？安装个依赖，为何需要使用 grunt 呢?

npm install
npm WARN engine karma@0.12.32: wanted: {"node":"~0.8 || ~0.10"} (current: {"node":"0.12.1","npm"
:"2.9.0"})
npm WARN peerDependencies The peer dependency mocha@* included from karma-mocha will no
npm WARN peerDependencies longer be automatically installed to fulfill the peerDependency
npm WARN peerDependencies in npm 3+. Your application will need to depend on it explicitly.
npm WARN peerDependencies The peer dependency chai@* included from karma-chai will no
npm WARN peerDependencies longer be automatically installed to fulfill the peerDependency
npm WARN peerDependencies in npm 3+. Your application will need to depend on it explicitly.
npm WARN optional dep failed, continuing fsevents@0.3.6
\


> grunt-autoprefixer@0.4.2 postinstall E:\xxxxxx\node_modules\grunt-autoprefixer