docs(client): fix HTTP/2 max concurrent stream link to spec (#4037)

Author: dentiny

src/client/conn/http2.rs

@@ -387,7 +387,7 @@ where
     ///
     /// See [Section 5.1.2] in the HTTP/2 spec for more details.
     ///
-    /// [Section 5.1.2]: https://http2.github.io/http2-spec/#rfc.section.5.1.2
+    /// [Section 5.1.2]: https://httpwg.org/specs/rfc7540.html#rfc.section.5.1.2
     pub fn max_concurrent_streams(&mut self, max: impl Into<Option<u32>>) -> &mut Self {
         self.h2_builder.max_concurrent_streams = max.into();
         self