erlang erlang@27: add ex_doc livecheck

[cho-m]

Not sure about best way to handle the OTP version in ex_doc_link.

For now, went with including the entire filename which seemed to work (will need to wait for next version to verify):

❯ brew lc -r --autobump erlang
erlang: 28.4.1 ==> 28.4.1
  html: 28.4.1 ==> 28.4.1
  ex_doc: 0.39.3/ex_doc_otp_27 ==> 0.39.3/ex_doc_otp_27

Alternatively, could ignore OTP version, but this would require manual update on major releases. Automatically bumping it would reduce maintenance.