[build] xtask: upgrade min rust version

rust-bins/xtask/src/main.rs

@@ -17,7 +17,7 @@ use anyhow::Result;
 use std::process::{Command, Output};
 use structopt::StructOpt;
 
-const MIN_RUST_VERTION: &str = "1.47.0";
+const MIN_RUST_VERTION: &str = "1.50.0";
 const NODE_VERSION: &str = "10.22.1";
 const NVM_VERSION: &str = "0.35.3";