Update README.md to include latest pulsar version (streamnative#333)

Co-authored-by: Rui Fu <freeznet@users.noreply.github.com>

Author: 2 people

README.md

@@ -22,7 +22,7 @@ Add the following dependencies in your `Cargo.toml`:
 
 ```toml
 futures = "0.3"
-pulsar = "5.1"
+pulsar = "6.3.1"
 tokio = "1.0"
 ```