libct: fix a comment

Do not refer to the function which was removed.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/standard_init_linux.go

@@ -167,7 +167,7 @@ func (l *linuxStandardInit) Init() error {
 		}
 	}
 
-	// Tell our parent that we're ready to Execv. This must be done before the
+	// Tell our parent that we're ready to exec. This must be done before the
 	// Seccomp rules have been applied, because we need to be able to read and
 	// write to a socket.
 	if err := syncParentReady(l.pipe); err != nil {