Link to eRFC for custom test frameworks

Author: fitzgen

text/007-2019-roadmap.md

@@ -263,10 +263,10 @@ binaries. Concretely, we should
 
 * add benchmarking support to `wasm-bindgen-test`, and
 
-* make `wasm-bindgen-test` future-compatible with the eRFC for custom test
-  frameworks, paving the way forward for making regular `#[test]` and `#[bench]`
-  Just Work™ with Wasm instead of requiring the use of
-  `#[wasm_bindgen_test]` instead.
+* make `wasm-bindgen-test` future-compatible with the [eRFC for custom test
+  frameworks](https://github.com/rust-lang/rust/issues/50297), paving the way
+  forward for making regular `#[test]` and `#[bench]` Just Work™ with Wasm
+  instead of requiring the use of `#[wasm_bindgen_test]` instead.
 
 # Rationale, Drawbacks, and Alternatives