bump tokio-util to 0.7

along with the rest of tokio/futures/hyper/openssl being updated - this
is the only one we explicitly depend on that had a non-compatible
version number.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

proxmox-backup-client/Cargo.toml

@@ -15,7 +15,7 @@ serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 tokio = { version = "1.6", features = [ "rt", "rt-multi-thread" ] }
 tokio-stream = "0.1.0"
-tokio-util = { version = "0.6", features = [ "codec", "io" ] }
+tokio-util = { version = "0.7", features = [ "codec", "io" ] }
 xdg = "2.2"
 zstd = { version = "0.6", features = [ "bindgen" ] }