Drop support for Ruby 3.0 (#357)

Author: olbrich

.github/workflows/tests.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ruby: ['3.0', '3.1', '3.2', '3.3', 'jruby-9.4']
+        ruby: ['3.1', '3.2', '3.3', 'jruby-9.4']
     env:
       BUNDLE_WITHOUT: optional
     steps:

.ruby-version

@@ -1 +1 @@
-3.0.6
+3.1.6

.tool-versions

@@ -1,2 +1,2 @@
 java adoptopenjdk-18.0.1+10
-ruby 3.0.6
+ruby 3.1.6

Gemfile.lock

@@ -3,7 +3,6 @@ PATH
   specs:
     ruby-units (4.1.0)
 
-
 GEM
   remote: https://rubygems.org/
   specs:

README.md

@@ -317,6 +317,10 @@ calculations. This in turn can have a negative impact on performance. The design
 of ruby-units has emphasized accuracy over speed. YMMV if you are doing a lot of
 math involving units.
 
+## Support Policy
+
+Only currently maintained versions of ruby and jruby are supported.
+
 ## License
 
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