title: Can't send attach files with SwiftMailer and Symfony3
body: <p>Hollo,
  I try to send mail with <strong>symfony3</strong> using <strong>SwiftMailer</strong>. Everything work like a charm when i don't include attach file. 
  When i try to attach file, email isn't sent and no error is generated.
  I don't know if it's due to an error in file path but the file is correctly located in /doc/temp directory in Symfony <strong>web</strong> directory.</p>
  
  <p>My source code is bellow: </p>
  
  <pre><code>            $message =  \Swift_Message::newInstance()
                  -&gt;setSubject("Subject")
                  -&gt;setFrom("from@gmail.com")
                  -&gt;setTo("to@gmail.com")
              ;
  
              $message-&gt;setBody($this-&gt;renderView(
                  'xxxx.email.twig'
              ), "text/html");
  
              $message-&gt;attach(\Swift_Attachment::fromPath('/doc/temp/file.pdf'));
  
              $this-&gt;get('mailer')-&gt;send($message);
  </code></pre>
  
  <p>Thanks for your help and sorry if i have some mistakes, english isn't my main language.</p>