Fix: remove uneeded futures crate

Author: samparsky

Cargo.lock

@@ -25,8 +25,7 @@ sha2 = "0.8.0"
 base64 = "0.10.1"
 lazy_static = "1.4.0"
 # Futures
-futures_legacy = { version = "0.3.1", package = "futures" }
-futures-preview = { version = "=0.3.0-alpha.19", features = ["compat"]}
+futures = { version = "0.3.1", features = ["compat"] }
 
 [dev-dependencies]
 byteorder = "1.3"