bump min Squib version

CHANGELOG.md

@@ -11,6 +11,7 @@ Features:
 
 Compatibility:
 * When saving PNGs with sprues, outputs start counting at zero - which is more consistent with the rest of Squib.
+* Minimum Ruby is now 2.5. NOTE: Ruby 3.0 is coming Christmas 2020!! Check it out.
 
 Bugs:
 * Extra page/no page issue with sprues (#320)

squib.gemspec

@@ -7,7 +7,7 @@ Gem::Specification.new do |spec|
   spec.specification_version = 2 if spec.respond_to? :specification_version=
   spec.required_rubygems_version = Gem::Requirement.new('>= 0') if spec.respond_to? :required_rubygems_version=
   spec.rubygems_version = '2.2.2'
-  spec.required_ruby_version = '>= 2.4.0'
+  spec.required_ruby_version = '>= 2.5.0'
 
   spec.name          = 'squib'
   spec.version       = Squib::VERSION