Add plus character + to legal mime subtype

For example, the following mime type (used for epub) is not recognized given the current regexp: `application/epub+zip`

src/Symfony/Component/HttpFoundation/File/MimeType/FileBinaryMimeTypeGuesser.php

@@ -89,7 +89,7 @@ class FileBinaryMimeTypeGuesser implements MimeTypeGuesserInterface
 
         $type = trim(ob_get_clean());
 
-        if (!preg_match('#^([a-z0-9\-]+/[a-z0-9\-\.]+)#i', $type, $match)) {
+        if (!preg_match('#^([a-z0-9\-]+/[a-z0-9\-\+\.]+)#i', $type, $match)) {
             // it's not a type, but an error message
             return null;
         }