Ruby security updates (#433)

* Upgrade to Ruby 3.1.7

* Upgrade to Ruby 3.2.8

Author: ajhodgson

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 3.1.3 (not yet released)
- * 
+ * Upgraded to Ruby 3.1.7 (from 3.1.6)
+ * Upgraded to Ruby 3.2.8 (from 3.2.7)
 
 ## 3.1.2 (release date: 2025-02-19)
  * Upgraded to Ruby 3.4.2 (from 3.4.1).

README.md

@@ -94,7 +94,7 @@ Basics (learn more at [baseimage-docker](http://phusion.github.io/baseimage-dock
 
 Language support:
 
- * Ruby 3.1.6, 3.2.7, 3.3.7, 3.4.2 and JRuby 9.3.15.0 and 9.4.9.0.
+ * Ruby 3.1.7, 3.2.8, 3.3.7, 3.4.2 and JRuby 9.3.15.0 and 9.4.9.0.
    * RVM is used to manage Ruby versions. [Why RVM?](#why_rvm)
    * 3.4.2 is configured as the default.
    * JRuby is installed from source, but we register an APT entry for it.
@@ -452,10 +452,10 @@ We use [RVM](https://rvm.io/) to install and to manage Ruby interpreters. Becaus
 The default Ruby (what the `/usr/bin/ruby` command executes) is the latest Ruby version that you've chosen to install. You can use RVM select a different version as default.
 
 ```dockerfile
-# Ruby 3.1.6
-RUN bash -lc 'rvm --default use ruby-3.1.6'
-# Ruby 3.2.7
-RUN bash -lc 'rvm --default use ruby-3.2.7'
+# Ruby 3.1.7
+RUN bash -lc 'rvm --default use ruby-3.1.7'
+# Ruby 3.2.8
+RUN bash -lc 'rvm --default use ruby-3.2.8'
 # Ruby 3.3.7
 RUN bash -lc 'rvm --default use ruby-3.3.7'
 # Ruby 3.4.2