Bump minimum Ruby to 2.7 and refresh README compatibility info

- gemspec: required_ruby_version >= 2.7.0 (matches the CI matrix floor
  established by the modernization PR; drops 2.2..2.6 which are EOL)
- README badges: show "ruby >= 2.7" / "ruby 2.7+"
- Compatibility table:
  - "unreleased" row reflects current main: ruby >= 2.7,
    activemodel >= 6.0 (tested through Rails 8.1 + edge)
  - 4.5.1 -> 4.5.2 to match the last published release
  - Fix small typo in pt-BR header ("u-attributes-" -> "u-attributes")

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: serradura

README.md

@@ -6,7 +6,7 @@
 </p>
 
 <p align="center">
-  <img src="https://img.shields.io/badge/ruby->%3D%202.2.0-ruby.svg?colorA=99004d&colorB=cc0066" alt="Ruby">
+  <img src="https://img.shields.io/badge/ruby->%3D%202.7-ruby.svg?colorA=99004d&colorB=cc0066" alt="Ruby">
 
   <a href="https://rubygems.org/gems/u-case">
     <img alt="Gem" src="https://img.shields.io/gem/v/u-case.svg?style=flat-square">
@@ -101,8 +101,8 @@ unreleased| https://github.com/serradura/u-case/blob/main/README.md
 
 | u-case         | branch  | ruby     | activemodel   | u-attributes  |
 | -------------- | ------- | -------- | ------------- | ------------- |
-| unreleased     | main    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
-| 4.5.1          | v4.x    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
+| unreleased     | main    | >= 2.7   | >= 6.0        | >= 2.7, < 3.0 |
+| 4.5.2          | v4.x    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
 | 3.1.0          | v3.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |
 | 2.6.0          | v2.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |
 | 1.1.0          | v1.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |

README.pt-BR.md

@@ -6,7 +6,7 @@
 </p>
 
 <p align="center">
-  <img src="https://img.shields.io/badge/ruby-2.2+-ruby.svg?colorA=99004d&colorB=cc0066" alt="Ruby">
+  <img src="https://img.shields.io/badge/ruby-2.7+-ruby.svg?colorA=99004d&colorB=cc0066" alt="Ruby">
 
   <a href="https://rubygems.org/gems/u-case">
     <img alt="Gem" src="https://img.shields.io/gem/v/u-case.svg?style=flat-square">
@@ -97,10 +97,10 @@ unreleased| https://github.com/serradura/u-case/blob/main/README.md
 
 ## Compatibilidade
 
-| u-case         | branch  | ruby     | activemodel   | u-attributes- |
+| u-case         | branch  | ruby     | activemodel   | u-attributes  |
 | -------------- | ------- | -------- | ------------- | ------------- |
-| unreleased     | main    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
-| 4.5.1          | v4.x    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
+| unreleased     | main    | >= 2.7   | >= 6.0        | >= 2.7, < 3.0 |
+| 4.5.2          | v4.x    | >= 2.2.0 | >= 3.2, < 7.0 | >= 2.7, < 3.0 |
 | 3.1.0          | v3.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |
 | 2.6.0          | v2.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |
 | 1.1.0          | v1.x    | >= 2.2.0 | >= 3.2, < 6.1 |        ~> 1.1 |

u-case.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |spec|
   spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
   spec.require_paths = ['lib']
 
-  spec.required_ruby_version = '>= 2.2.0'
+  spec.required_ruby_version = '>= 2.7.0'
 
   spec.add_runtime_dependency 'kind', '>= 5.6', '< 6.0'
   spec.add_runtime_dependency 'u-attributes', '>= 2.7', '< 3.0'