Typo in BAN configuration

Submitted by:	Clement Gautier via github

doc/sphinx/users-guide/purging.rst

@@ -103,7 +103,7 @@ You can also add bans to Varnish via HTTP. Doing so requires a bit of VCL::
 			  return(synth(403, "Not allowed."));
 		  }
 		  ban("req.http.host == " + req.http.host +
-		        "&& req.url == " + req.url);
+		        " && req.url == " + req.url);
 
 		  # Throw a synthetic page so the
                   # request won't go to the backend.