title: failed to parse json when adding grunt to dev-dependencies
body: <p>I have a simple package.json and am trying to add grunt to my project. I've done this many times but have never encountered this problem</p>
  
  <p>My <code>package.json</code>:</p>
  
  <pre><code>{
    "name": "express-todo",
    "main": "server.js",
    "dependencies": {
      "body-parser": "^1.0.2",
      "express": "^4.1.1",
      "jade": "^1.3.1",
      "mongoose": "^3.8.8",
      "nodemon": "^1.0.17",
      "request": "^2.34.0"
    }
  }
  </code></pre>
  
  <p>Then from the command line i get the error:</p>
  
  <pre><code>$ npm install grunt --save-dev
  npm WARN package.json express-todo@ No repository field.
  npm http GET https://registry.npmjs.org/grunt
  npm http 304 https://registry.npmjs.org/grunt
  npm ERR! Failed to parse json
  npm ERR! Unexpected end of input
  npm ERR! File: /home/jasonshark/.npm/grunt/0.4.4/package/package.json
  npm ERR! Failed to parse package.json data.
  npm ERR! package.json must be actual JSON, not just JavaScript.
  npm ERR! 
  npm ERR! This is not a bug in npm.
  npm ERR! Tell the package author to fix their package.json file. JSON.parse
  
  npm ERR! System Linux 3.2.0-61-generic-pae
  npm ERR! command "/usr/bin/node" "/usr/bin/npm" "install" "grunt" "--save-dev"
  npm ERR! cwd /home/jasonshark/Projects/express-todo
  npm ERR! node -v v0.10.28
  npm ERR! npm -v 1.4.9
  npm ERR! file /home/jasonshark/.npm/grunt/0.4.4/package/package.json
  npm ERR! code EJSONPARSE
  npm ERR! 
  npm ERR! Additional logging details can be found in:
  npm ERR!     /home/jasonshark/Projects/express-todo/npm-debug.log
  npm ERR! not ok code 0
  </code></pre>