title: Composer install: error on temporary file
body: <p>I have a problem with windows 10 and composer (last version).
  When I want to execute command "composer install" in my project, a symphony error is thrown:</p>
  
  <pre><code>[Symfony\Component\Process\Exception\RuntimeException]
  A temporary file could not be opened to write the process output to, verify that your TEMP environment variable is writable
  </code></pre>
  
  <p>My TEMP variable is "%USERPROFILE%\AppData\Local\Temp".
  The folder exists and permissions are good.</p>
  
  <p>Can anyone help me to find the problem please?</p>
  
  <p>Thank you.</p>