message: doc: fix rustdoc warning about automatic link
  PR
diff: @@ -31,7 +31,7 @@ considerably more complex than one might expect out of a DFA. A number of
  tricks are employed to make it fast. Tread carefully.
  N.B. While this implementation is heavily commented, Russ Cox's series of
  -articles on regexes is strongly recommended: https://swtch.com/~rsc/regexp/
  +articles on regexes is strongly recommended: <https://swtch.com/~rsc/regexp/>
  (As is the DFA implementation in RE2, which heavily influenced this
  implementation.)
  */
  