title: RuntimeException in composer update
body: <p>I got error when I do composer update, it says <code>RuntimeException</code></p>
  
  <pre><code>$ composer update
  Loading composer repositories with package information
  Updating dependencies (including require-dev)
  - Removing mews/purifier (1.0.1)
  
  
  
  [RuntimeException]
  Could not delete /var/www/myproj.com/protected/vendor/mews/purifier/LICENCE.md:
  
  
  
  update [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--lock] [--no-plugins] [--no-custom-installers] [--no-autoloader] [--no-scripts] [--no-progress] [--with-dependencies] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader] [--ignore-platform-reqs] [--prefer-stable] [--prefer-  lowest] [packages1] ... [packagesN]
  </code></pre>
  
  <p>does anyone have an idea about my case?</p>