在npm install中出现以下错误，已经安装了grunt
npm WARN grunt-contrib-clean@0.5.0 requires a peer of grunt@~0.4.0 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-contrib-concat@0.3.0 requires a peer of grunt@~0.4.0 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-contrib-copy@0.5.0 requires a peer of grunt@~0.4.0 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-contrib-cssmin@0.7.0 requires a peer of grunt@~0.4.1 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-contrib-htmlmin@0.1.3 requires a peer of grunt@~0.4.0 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-dom-munger@3.4.0 requires a peer of grunt@~0.4.1 but none is installed. You must install peer dependencies yourself.
npm WARN grunt-ng-annotate@0.5.0 requires a peer of grunt@~0.4.1 but none is installed. You must install peer dependencies yourself.