Removed to support Ruby 2.3

  https://travis-ci.org/ruby/date/jobs/314561806

Author: hsbt

.travis.yml

@@ -1,7 +1,6 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.3.5
   - 2.4.2
   - ruby-head
 before_install: gem install bundler

date.gemspec

@@ -2,7 +2,7 @@
 Gem::Specification.new do |s|
   s.name = "date"
   s.version = '1.0.0'
-  s.date = '2017-12-08'
+  s.date = '2017-12-11'
   s.summary = "A subclass of Object includes Comparable module for handling dates."
   s.description = "A subclass of Object includes Comparable module for handling dates."
 
@@ -13,7 +13,7 @@ Gem::Specification.new do |s|
     "ext/date/zonetab.h", "ext/date/zonetab.list"
   ]
   s.extensions = "ext/date/extconf.rb"
-  s.required_ruby_version = ">= 2.3.0"
+  s.required_ruby_version = ">= 2.4.0"
 
   s.authors = ["Tadayoshi Funaba"]
   s.email = [nil]