fix old rust-lang nursery reference

Author: lqd

Cargo.toml

@@ -4,7 +4,7 @@ version     = "0.7.0"
 authors     = ["The Rust Project Developers", "Polonius Developers"]
 description = "Core definition for the Rust borrow checker"
 license     = "Apache-2.0/MIT"
-repository  = "https://github.com/rust-lang-nursery/polonius"
+repository  = "https://github.com/rust-lang/polonius"
 readme      = "README.md"
 keywords    = ["compiler", "borrowck", "datalog"]
 edition     = "2018"