make link clickable

Author: Lukas Markeffsky

compiler/rustc_error_codes/src/error_codes/E0794.md

@@ -59,6 +59,6 @@ In the definition of `bar`, the lifetime parameter `'a` is late-bound, while
 where `'a` is universally quantified and `'b` is substituted by a specific
 lifetime. It is not allowed to explicitly specify early-bound lifetime
 arguments when late-bound lifetime parameters are present (as for `bar_fn2`,
-see issue #42868: https://github.com/rust-lang/rust/issues/42868), although the
+see [issue #42868](https://github.com/rust-lang/rust/issues/42868)), although the
 types that are constrained by early-bound parameters can be specified (as for
 `bar_fn3`).