Drop Ruby 2.5 support

Author: shugo

.github/workflows/ubuntu.yml

@@ -6,7 +6,7 @@ jobs:
   test:
     strategy:
       matrix:
-        ruby: [ head, 2.7, 2.6, 2.5 ]
+        ruby: [ head, 3.1, 2.7, 2.6, 2.5 ]
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v2

.github/workflows/windows.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: windows-latest
     strategy:
       matrix:
-        ruby: [ 'mingw', 'mswin', '2.7', '2.6', '2.5' ]
+        ruby: [ 'mingw', 'mswin', '3.1', '2.7', '2.6' ]
     steps:
     - uses: actions/checkout@v2
       with:

curses.gemspec

@@ -9,7 +9,7 @@ Gem::Specification.new { |s|
   s.files = `git ls-files --recurse-submodules -z`.split("\x0")
   s.extensions = ["ext/curses/extconf.rb"]
   s.require_path = "lib"
-  s.required_ruby_version = Gem::Requirement.new('>= 2.1.0')
+  s.required_ruby_version = Gem::Requirement.new('>= 2.6.0')
   s.licenses = ['Ruby', 'BSD-2-Clause']
   s.add_development_dependency 'bundler'
   s.add_development_dependency 'rake'