title: Updating Vendors Symfony2
body: <p>Hi I donwloaded and installed Symfony2 using the archive but I had a problem during the vendor's updating.
  In my principal folder Symfony I run the command <code>php composer.phar install</code> but I obtained the following error</p>
  
  <p>Loading composer repositories with package information
  Installing dependencies (including require-dev) from lock file
  Your requirements could not be resolved to an installable set of packages.</p>
  
  <p>Problem 1<br>
      - sensiolabs/security-checker v2.0.0 requires ext-curl * -> the requested PHP extension curl is missing from your system.<br>
      - sensiolabs/security-checker v2.0.0 requires ext-curl * -> the requested PHP extension curl is missing from your system.<br>
      - Installation request for sensiolabs/security-checker v2.0.0 -> satisfiable by sensiolabs/security-checker[v2.0.0].</p>
  
  <p>What can I do?</p>