我用下面的命令安装Express.js:

sudo npm install -g express

我得到以下警告:

npm WARN package.json range-parser@0.0.4 No repository field.
npm WARN package.json fresh@0.1.0 No repository field.
npm WARN package.json methods@0.0.1 No repository field.
npm WARN package.json methods@0.0.1 No readme data.
npm WARN package.json cookie-signature@1.0.1 No repository field.
npm WARN package.json send@0.1.0 No repository field.
npm WARN package.json pause@0.0.1 No repository field.
npm WARN package.json bytes@0.2.0 No repository field.
npm WARN package.json github-url-from-git@1.1.1 No repository field.
npm WARN package.json assert-plus@0.1.2 No repository field.
npm WARN package.json ctype@0.5.2 No repository field.

为什么我有上述警告?我应该担心吗?