Project: Adjust minimum dependency to Ruby >= 2.5

Author: amotl

.rubocop.yml

@@ -4,4 +4,4 @@ require: rubocop-rspec
 
 AllCops:
   NewCops: enable
-  TargetRubyVersion: 2.4
+  TargetRubyVersion: 2.5

crate_ruby.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |spec|
   spec.description   = 'A Ruby library for the CrateDB HTTP interface with query support, DDL command and schema introspection shortcuts, and support for BLOB tables.'
   spec.homepage      = 'https://crate.io'
   spec.license       = 'Apache-2.0'
-  spec.required_ruby_version = '>= 2.4'
+  spec.required_ruby_version = '>= 2.5'
 
   spec.files         = Dir['lib/**/*']
   spec.executables   = spec.files.grep(%r{^bin/}) { |f| File.basename(f) }