title: why the difference in node_modules when npm install is run multiple times?
body: <p>I have a package.json file which has dependencies defined as below (i.e im using  exact versions for every package):</p>
  
  <pre><code> "dependencies": {
          "async": "0.9.2",
          "body-parser": "1.15.1",
          "cookie-parser": "1.4.2",
          "csvtojson": "0.3.21",
          "express": "4.13.4",
          "jsonwebtoken": "7.1.9",
          "lodash": "4.16.6",
          "mongodb": "1.4.40",
          "request": "2.78.0",
          "seneca": "3.3.0",
          "seneca-amqp-transport": "2.1.0"
      }
  </code></pre>
  
  <p>When i run npm install on this package.json file twice and compare the node_modules folders generated, i see differences in the folder. The difference is usually in the readme,_from and url field of the packages (Refer attachments for the same).</p>
  
  <p><a href="https://i.stack.imgur.com/q1ZMW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/q1ZMW.png" alt="readme difference"></a></p>
  
  <p><a href="https://i.stack.imgur.com/2cTZT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2cTZT.png" alt="url difference"></a></p>
  
  <p><a href="https://i.stack.imgur.com/j1V2r.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/j1V2r.png" alt="from difference"></a></p>
  
  <ol>
  <li>Is this expected? </li>
  <li>Does this difference have any impact on my application ?</li>
  <li>Is there a way to avoid it?</li>
  </ol>