Update GitHub Actions (rust-random#1263)

* examples/rayon-monte-carlo.rs: remove execute bit of file metadata

* Document in README that MSRV is 1.51.0

This was changed in rust-random#1246

* Update GitHub Actions

README.md

@@ -5,7 +5,7 @@
 [![Book](https://img.shields.io/badge/book-master-yellow.svg)](https://rust-random.github.io/book/)
 [![API](https://img.shields.io/badge/api-master-yellow.svg)](https://rust-random.github.io/rand/rand_distr)
 [![API](https://docs.rs/rand_distr/badge.svg)](https://docs.rs/rand_distr)
-[![Minimum rustc version](https://img.shields.io/badge/rustc-1.36+-lightgray.svg)](https://github.com/rust-random/rand#rust-version-requirements)
+[![Minimum rustc version](https://img.shields.io/badge/rustc-1.51+-lightgray.svg)](https://github.com/rust-random/rand#rust-version-requirements)
 
 Implements a full suite of random number distribution sampling routines.