Update Rust version in README (#200)

Author: k-sareen

README.md

@@ -16,7 +16,7 @@ Please make sure your dev machine satisfies those prerequisites.
 ### Before you continue
 
 The minimal supported Rust version for MMTk-OpenJDK binding is 1.57.0. Make sure your Rust version is higher than this. We test MMTk-OpenJDK
-binding with Rust 1.59.0 (as specified in [`rust-toolchain`](mmtk/rust-toolchain)).
+binding with Rust 1.66.1 (as specified in [`rust-toolchain`](mmtk/rust-toolchain)).
 You may also need to use ssh-agent to authenticate with github (see [here](https://github.com/rust-lang/cargo/issues/3487) for more info):
 
 ```console