Fix incorrect link in v10 release notes.
As noted by M. Justin.
Also, to keep the HEAD and REL_10 versions of release-10.sgml in sync,
back-patch the effects of
c29c57890 on that file. We have a bigger
problem there though :-(
Discussion: https://postgr.es/m/CALtA7pmsQyTTD3fC2rmfUWgfivv5sCJJ84PHY0F_5t_SRc07Qg@mail.gmail.com
Discussion: https://postgr.es/m/
6d137bd0-eef6-1d91-d9b8-
1a5e9195a899@2ndquadrant.com