Fix broken link to Rust's code of conduct (#2810)

CODE_OF_CONDUCT.md

@@ -1,3 +1,3 @@
 # Code of Conduct
 
-The Anchor repository follows the Rust [Code of Conduct](https://www.rust-lang.org/conduct.html).
+The Anchor repository follows the Rust [Code of Conduct](https://www.rust-lang.org/policies/code-of-conduct).