Mark gems as requiring Ruby 2.3

Author: byroot

redis.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
   s.files         = Dir["CHANGELOG.md", "LICENSE", "README.md", "lib/**/*"]
   s.executables   = `git ls-files -- exe/*`.split("\n").map{ |f| File.basename(f) }
 
-  s.required_ruby_version = '>= 2.2.2'
+  s.required_ruby_version = '>= 2.3.0'
 
   s.add_development_dependency("mocha")
   s.add_development_dependency("hiredis")