dev: update CI and style settings (#258)

Merge pull request 258

Author: jekyllbot

.rubocop.yml

@@ -4,7 +4,7 @@ inherit_gem:
   rubocop-jekyll: .rubocop.yml
 
 AllCops:
-  TargetRubyVersion: 2.3
+  TargetRubyVersion: 2.4
   Include:
     - lib/**/*.rb
 

.travis.yml

@@ -2,8 +2,8 @@ language: ruby
 cache: bundler
 sudo: false
 rvm:
-- 2.5
-- 2.3
+- 2.6
+- 2.4
 env:
   global:
   - NOKOGIRI_USE_SYSTEM_LIBRARIES=true

Gemfile

@@ -3,6 +3,4 @@
 source "https://rubygems.org"
 gemspec
 
-if ENV["JEKYLL_VERSION"]
-  gem "jekyll", "~> #{ENV["JEKYLL_VERSION"]}"
-end
+gem "jekyll", "~> #{ENV["JEKYLL_VERSION"]}" if ENV["JEKYLL_VERSION"]

jekyll-feed.gemspec

@@ -21,10 +21,10 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = ">= 2.3.0"
 
   spec.add_dependency "jekyll", "~> 3.3"
-  spec.add_development_dependency "bundler", "~> 1.15"
+  spec.add_development_dependency "bundler"
   spec.add_development_dependency "nokogiri", "~> 1.6"
   spec.add_development_dependency "rake", "~> 12.0"
   spec.add_development_dependency "rspec", "~> 3.0"
-  spec.add_development_dependency "rubocop-jekyll", "~> 0.4"
+  spec.add_development_dependency "rubocop-jekyll", "~> 0.5"
   spec.add_development_dependency "typhoeus", ">= 0.7", "< 2.0"
 end