Deps: Bump xsalsa20poly1305 version -> 0.7

This dependency upgrade (at last) resolves the duplicated rand_core versions present in builds. This was tested using `cargo make ready`.

Cargo.toml

@@ -126,7 +126,7 @@ features = ["v4"]
 
 [dependencies.xsalsa20poly1305]
 optional = true
-version = "0.6"
+version = "0.7"
 
 [dev-dependencies]
 criterion = "0.3"

src/driver/connection/mod.rs

@@ -319,7 +319,7 @@ async fn init_cipher(client: &mut WsStream, mode: CryptoMode) -> Result<Cipher>
                     return Err(Error::CryptoModeInvalid);
                 }
 
-                return Ok(Cipher::new_varkey(&desc.secret_key)?);
+                return Ok(Cipher::new_from_slice(&desc.secret_key)?);
             },
             other => {
                 debug!(