man: virtfs-proxy-helper: Rework awkward sentence

There was a 'capbilities' typo in this man page. This commit
reformulates the sentence the typo was in to make it easier to grasp.
This is based on a suggestion from Eric Blake.

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

fsdev/virtfs-proxy-helper.texi

@@ -28,8 +28,8 @@ QEMU and proxy helper communicate using this socket. QEMU proxy fs
 driver sends filesystem request to proxy helper and receives the
 response from it.
 
-Proxy helper is designed so that it can drop the root privilege with
-retaining capbilities needed for doing filesystem operations only.
+The proxy helper is designed so that it can drop root privileges except
+for the capabilities needed for doing filesystem operations.
 
 @end table
 @c man end