title: npm: "Error: invalid version: 1.0" while installing grunt plugins
body: <p>While yesterday all works fine, today i am getting the printed error below, when i try to install a grunt plugin, wether it is a official grunt contrib or vendor plugin.
  I am running grunt v0.4, node v0.8.20 and npm v1.2.11, System X 10.8.2.</p>
  
  <pre><code>npm install grunt-&lt;plugin&gt;-&lt;name&gt; --save-dev
  npm ERR! Error: invalid version: 1.0
  npm ERR!     at validVersion (/usr/local/lib/node_modules/npm/node_modules/read-package-json/read-json.js:590:40)
  npm ERR!     at final (/usr/local/lib/node_modules/npm/node_modules/read-package-json/read-json.js:342:23)
  ...
  </code></pre>
  
  <p>What suprises me is that also official grunt contrib plugins (grunt-contrib-xxx) fails to install altough i expect it has a proper semver version syntax. npm-debug.log shows nothing additional to the verbose output in the console.</p>
  
  <p>Any hints are appreciated.</p>
  
  <p>Thx in advance
  felic</p>