Cargo update and fix clap changes

To support the latest beta version of clap (v3.0.0-beta.4) small
changes were necessary.

src/main.rs

@@ -7,8 +7,10 @@ mod sysv;
 #[derive(Clap, Debug)]
 enum Backend {
     /// Handle POSIX message queues
+    #[clap(subcommand)]
     Posix(PosixCommand),
     /// Handle SysV message queues
+    #[clap(subcommand)]
     Sysv(SysvCommand),
 }
 
@@ -35,7 +37,7 @@ enum SysvCommand {
     version = crate_version!(),
     author = crate_authors!(", "),
     setting = AppSettings::SubcommandRequiredElseHelp,
-    global_setting = AppSettings::VersionlessSubcommands,
+    global_setting = AppSettings::PropagateVersion,
     global_setting = AppSettings::InferSubcommands,
 )]
 struct Opts {