npm install dosen't install dev dependencies - npm

Question

I have a project where I use npm for handling dependencies. The project is bundled with Webpack and will run on the client (it's built for using gh-pages for hosting) with no production dependencies. Therefore I have only devDependencies in my package.json. However, when I run npm install nothing gets installed. When I run npm install --dev my dependencies gets installed as they are supposed to. Since --dev is deprecated I tried with npm install --only=dev as well, however nothing gets installed then either! Is there something broken in my package.json (inserted below) or am I misunderstanding npm?
{
"name": "Boilerplate",
"version": "0.0.1",
"description": "A boilerplate to quickly get started with an offline first React/Redux app",
"repository": {
"type": "git",
"url": "https://github.com/OskarKlintrot/Offline-First-React-And-Redux-Boilerplate"
},
"scripts": {
"start": "webpack-dev-server",
"build": "webpack --progress --colors --production"
},
"private": true,
"devDependencies": {
"babel-core": "^6.2.1",
"babel-eslint": "^4.0.5",
"babel-loader": "^6.2.0",
"babel-polyfill": "^6.2.0",
"babel-preset-es2015": "^6.1.18",
"babel-preset-react": "^6.1.18",
"babel-preset-stage-1": "^6.1.18",
"eslint": "^1.1.0",
"eslint-loader": "^1.0.0",
"eslint-plugin-react": "^3.13.1",
"file-loader": "^0.8.5",
"history": "^1.17.0",
"react": "^0.14.2",
"react-dom": "^0.14.2",
"react-hot-loader": "^1.3.0",
"react-mdl": "^1.0.2",
"react-redux": "^4.0.4",
"react-router": "^1.0.2",
"react-tap-event-plugin": "^0.2.1",
"redux": "^3.0.5",
"redux-devtools": "^3.0.0",
"redux-devtools-dock-monitor": "^1.0.1",
"redux-devtools-log-monitor": "^1.0.1",
"redux-history-transitions": "^1.0.0",
"redux-thunk": "^1.0.2",
"transfer-webpack-plugin": "^0.1.4",
"webpack": "^1.12.9",
"webpack-dev-server": "^1.14.0"
}
}