Switch default version of Ruby from 2.6 to 2.7.

For detailed list of changes, please check the Ruby website:
https://www.ruby-lang.org/en/news/2019/12/25/ruby-2-7-0-released/
https://www.ruby-lang.org/en/news/2020/03/31/ruby-2-7-1-released/
https://www.ruby-lang.org/en/news/2020/10/02/ruby-2-7-2-released/

How to upgrade is described in UPDATING entry 20201128.

PR:		244787
Submitted by:	meta@
Exp-Run:	https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=244787
Thanks to:	antoine, meta

Mk/bsd.default-versions.mk

@@ -103,7 +103,7 @@ PYTHON2_DEFAULT?=	2.7
 # Possible values: 3.6, 3.7, 3.8, 3.9
 PYTHON3_DEFAULT?=	3.7
 # Possible values: 2.5, 2.6, 2.7, 3.0
-RUBY_DEFAULT?=		2.6
+RUBY_DEFAULT?=		2.7
 # Possible values: rust, rust-nightly
 RUST_DEFAULT?=		rust
 # Possible values: 4.11, 4.12, 4.13

UPDATING

@@ -5,6 +5,30 @@ they are unavoidable.
 You should get into the habit of checking this file for changes each time
 you update your ports collection, before attempting any port upgrades.
 
+20201128:
+  AFFECTS: users of lang/ruby26
+  AUTHOR: mfechner@FreeBSD.org
+
+  The default ruby version has been updated from 2.6 to 2.7.
+
+  If you compile your own ports you may keep 2.6 as the default version by
+  adding the following lines to your /etc/make.conf file:
+
+  #
+  # Keep ruby 2.6 as default version
+  #
+  DEFAULT_VERSIONS+=ruby=2.6
+
+  If you wish to update to the new default version, you need to first stop any
+  software that uses ruby. Then, you will need to follow these steps, depending
+  upon how you manage your system.
+
+  If you use pkg, simply upgrade:
+  # pkg upgrade
+
+  If you do not use pkg, please check entry 20190420.
+  The description there should also work for this version.
+
 20201112:
   AFFECTS: users of net-mgmt/pushgateway
   AUTHOR: rhurlin@FreeBSD.org