Drop Ruby 3.1 support (#418)

Resolve #395

Author: Yang-33

.github/workflows/pull_request.yml

@@ -13,7 +13,9 @@ jobs:
     strategy:
       matrix:
         # https://www.ruby-lang.org/en/downloads/branches/
-        ruby: [ '3.1', '3.2', '3.3' ]
+        ruby:
+          - '3.2'
+          - '3.3'
     name: Ruby v${{ matrix.ruby }}
     steps:
     - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2

README.md

@@ -18,7 +18,7 @@ Also, generated documentation by YARD is available.
 - https://rubydoc.info/gems/line-bot-api
 
 ## Requirements
-This library requires Ruby 3.1 or later.
+This library requires Ruby 3.2 or later.
 
 ## Installation
 

README_v2.md

@@ -18,7 +18,7 @@ Also, generated documentation by YARD is available.
 - https://rubydoc.info/gems/line-bot-api
 
 ## Requirements
-This library requires Ruby 3.1 or later.
+This library requires Ruby 3.2 or later.
 
 ## Installation
 

line-bot-api.gemspec

@@ -17,7 +17,7 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.required_ruby_version     = '>= 2.4.0'
+  spec.required_ruby_version     = '>= 3.2.0'
 
   spec.add_dependency "multipart-post", "~> 2.4.1"