title: What's the difference between ~ and ^ in packagist
body: <p>I'm a bit confused the difference between '~' and '^' in packagist , </p>
  
  <p>code example in composer.json file:</p>
  
  <pre><code> "require": {
               "doctrine/dbal": "^2.6",      //this is using '^' symbol
               "garygreen/pretty-routes": "~0.0.6"    //this is using '~' symbol
              },
  </code></pre>
  
  <p>Can someone explain this for me ?</p>