databases/couchdb2: update to 2.3.1

[dch]

Summary

• tweak rc.d script to ensure coredumps can be retrieved if needed
• explicitly depend on OTP>=21.3 to skip BEAM coredumps observed in the wild
• drop OTP<20 option per above
• pet Makefile while here

Test Plan

poudriere OK on 12.0R amd64, x86, armv6, armv7 +
13.0-CURRENT amd64

lang/erlang  (build time only dependency) fails for 11.2 x64 & x86
but IMO shouldn't block this PR. I'll look into that later this
week.

[jrm]

• I see a failure because [[ http://pkg.awarnach.mathstat.dal.ca/build.html?mastername=12amd64-default&build=2019-03-18_10h55m02s | lang/erlang-runtime21 fails to fetch ]].
• The alignment looks strange. This is what I see.
  
• If the build is broken for 11.2, then it should be marked as such.

[dch]

[jrm]

You must have changed the tab width or made some other change in your configuration. Something is clearly up, since you changed the indentation on most lines in this revision. Here is what I see in /usr/bin/vi in a pristine jail.

[dch]

un-pet Makefile with correct tabstops

[jrm]

Are the RC3s in the filenames under libexec/couchdb2/lib/ an issue?