Bump required Ruby version to 2.7.0

Ruby 2.6 reached end-of-life in March 2022.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: nimmolo

superform.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |spec|
   spec.description = "A better way to customize and build forms for your Rails application"
   spec.homepage = "https://github.com/rubymonolith/superform"
   spec.license = "MIT"
-  spec.required_ruby_version = ">= 2.6.0"
+  spec.required_ruby_version = ">= 2.7.0"
 
   spec.metadata["allowed_push_host"] = "https://rubygems.org"