Updated the Ruby versions to 2.2.x, 2.3.x and 2.4.x.

Ruby < 2.2.x is no longer supported.

Also updated the Travis CI build to 2.2.x, 2.3.x and 2.4.x.

Author: evolve75

.travis.yml

@@ -7,23 +7,17 @@ before_install:
 bundler_args: --without development
 
 rvm:
-  - 1.8.7
-  - 1.9.2
-  - 1.9.3
-  - 2.0.0
-  - 2.2.1
-#  - ruby-head    # The latest Ruby, whatever version it happens to be.
-# - jruby-18mode
-# - jruby-19mode
-
+  - 2.2.9
+  - 2.3.6
+  - 2.4.3
 
 matrix:
   allow_failures:
     - rvm: rbx                  # rbx is still troublesome.
   include:
     - rvm: rbx
       gemfile: gemfiles/Gemfile.rbx
-    - rvm: 2.1.5
+    - rvm: 2.4.2
       env: COVERAGE=true
   exclude:
     - rvm: rbx

README.md

@@ -120,7 +120,7 @@ This example can also be found at
 
 ## REQUIREMENTS: ##
 
-* [Ruby][] 1.8.x, 1.9.x, 2.0.x, 2.1.x or 2.4.x.x
+* [Ruby][] 2.2.x, 2.3.x or 2.4.x
 
 
 * Run-time Dependencies:

rubytree.gemspec

@@ -20,7 +20,7 @@ Gem::Specification.new do |s|
   s.email                 = 'anupamsg@gmail.com'
   s.homepage              = 'http://rubytree.anupamsg.me'
 
-  s.required_ruby_version = '>=1.8.7'
+  s.required_ruby_version = '>=2.2'
 
   s.summary               = %q{A generic tree data structure.}
   s.description           = <<-EOF