Update URLs (#431)

Author: atouchet

mozjs/README.md

@@ -4,4 +4,4 @@ Rust bindings to SpiderMonkey
 
 [Documentation](https://doc.servo.org/mozjs/)
 
-See https://github.com/servo/mozjs/blob/master/README.md for build instructions.
+See https://github.com/servo/mozjs/blob/main/README.md for build instructions.

mozjs/src/lib.rs

@@ -19,8 +19,8 @@
 //! taking advantage of Rust's memory safety. For more about the Spidermonkey API, see the
 //! [API Reference][2] and the [User Guide][3] on MDN, and the [embedding examples][4] on GitHub.
 //!
-//! The code from User Guide sections [A minimal example](https://github.com/servo/mozjs/blob/master/mozjs/examples/minimal.rs) and
-//! [Running scripts](https://github.com/servo/mozjs/blob/master/mozjs/examples/eval.rs) are also included.
+//! The code from User Guide sections [A minimal example](https://github.com/servo/mozjs/blob/main/mozjs/examples/minimal.rs) and
+//! [Running scripts](https://github.com/servo/mozjs/blob/main/mozjs/examples/eval.rs) are also included.
 //!
 //! [1]: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey
 //! [2]: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/JSAPI_reference