Require earliest non EOL Ruby

https://www.ruby-lang.org/en/downloads/branches/

Author: agrberg

.rubocop.yml

@@ -2,7 +2,7 @@ require: 'rubocop-rspec'
 
 AllCops:
   NewCops: enable
-  TargetRubyVersion: 2.5
+  TargetRubyVersion: 2.6
 
 Layout/LineLength:
   Max: 120

cacheable.gemspec

@@ -15,6 +15,6 @@ Gem::Specification.new do |s|
   s.files       = Dir['lib/**/*', 'README.md', 'cache-adapters.md']
   s.homepage    = 'https://github.com/splitwise/cacheable'
   s.licenses    = 'MIT'
-  s.required_ruby_version = '>= 2.5.0'
+  s.required_ruby_version = '>= 2.6.0'
   s.metadata = {'rubygems_mfa_required' => 'true'}
 end

lib/cacheable/cache_adapters.rb

@@ -14,7 +14,7 @@ def lookup(adapter_name)
       private
 
       def class_name_for(string)
-        string.split('_').map { |name_part| "#{name_part[0].upcase}#{name_part[1..-1].downcase}" }.join
+        string.split('_').map { |name_part| "#{name_part[0].upcase}#{name_part[1..].downcase}" }.join
       end
     end
   end

lib/cacheable/version.rb

@@ -7,10 +7,8 @@ module VERSION
     TINY = 4
     PRE = nil
 
-    STRING = [MAJOR, MINOR, TINY, PRE].compact.join('.').freeze
-
     def self.to_s
-      STRING
+      [MAJOR, MINOR, TINY, PRE].compact.join('.').freeze
     end
   end
 end