Expand supported Ruby versions to include 2.6

.travis.yml

@@ -2,6 +2,7 @@ language: ruby
 rvm:
   - 2.4.5
   - 2.5.3
+  - 2.6.0
 cache:
   - bundler
 before_install:

CONTRIBUTING.md

@@ -8,7 +8,7 @@ There are a couple ways you can help improve webmention-cli:
 
 ## Getting Started
 
-webmention-cli is developed using Ruby 2.4.5 and is additionally tested against Ruby 2.5.3 using [Travis CI](https://travis-ci.com/jgarber623/webmention-cli).
+webmention-cli is developed using Ruby 2.4.5 and is additionally tested against Ruby 2.5.3 and 2.6.0 using [Travis CI](https://travis-ci.com/jgarber623/webmention-cli).
 
 Before making changes to webmention-cli, you'll want to install Ruby 2.4.5. It's recommended that you use a Ruby version managment tool like [rbenv](https://github.com/rbenv/rbenv), [chruby](https://github.com/postmodern/chruby), or [rvm](https://github.com/rvm/rvm). Once you've installed Ruby 2.4.5 using your method of choice, install the project's gems by running:
 

README.md

@@ -13,7 +13,7 @@
 
 Before installing and using webmention-cli, you'll want to have [Ruby](https://www.ruby-lang.org) 2.4 (or newer) installed. It's recommended that you use a Ruby version managment tool like [rbenv](https://github.com/rbenv/rbenv), [chruby](https://github.com/postmodern/chruby), or [rvm](https://github.com/rvm/rvm).
 
-webmention-cli is developed using Ruby 2.4.5 and is additionally tested against Ruby 2.5.3 using [Travis CI](https://travis-ci.com/jgarber623/webmention-cli).
+webmention-cli is developed using Ruby 2.4.5 and is additionally tested against Ruby 2.5.3 and 2.6.0 using [Travis CI](https://travis-ci.com/jgarber623/webmention-cli).
 
 ## Installation
 

webmention-cli.gemspec

@@ -4,7 +4,7 @@ $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
 require 'webmention_cli/version'
 
 Gem::Specification.new do |spec|
-  spec.required_ruby_version = ['>= 2.4', '< 2.6']
+  spec.required_ruby_version = ['>= 2.4', '< 2.7']
 
   spec.name          = 'webmention-cli'
   spec.version       = WebmentionCLI::VERSION