Remove support for Jekyll 2.x

Author: DirtyF

.rubocop.yml

@@ -1,6 +1,11 @@
 inherit_gem:
   jekyll: .rubocop.yml
 
+AllCops:
+  TargetRubyVersion: 2.1
+  Exclude:
+    - vendor/**/*
+
 Metrics/LineLength:
   Exclude:
     - spec/**/*

jekyll-gist.gemspec

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 lib = File.expand_path("lib", __dir__)
 
 $LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
@@ -12,7 +14,7 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://github.com/jekyll/jekyll-gist"
   spec.license       = "MIT"
 
-  spec.required_ruby_version = ">= 1.9.3"
+  spec.required_ruby_version = ">= 2.1"
 
   spec.files         = `git ls-files -z`.split("\x0")
   spec.executables   = spec.files.grep(%r!^bin/!) { |f| File.basename(f) }
@@ -21,8 +23,8 @@ Gem::Specification.new do |spec|
 
   spec.add_dependency "octokit", "~> 4.2"
   spec.add_development_dependency "bundler", "~> 1.6"
+  spec.add_development_dependency "jekyll", ">= 3.0"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec"
   spec.add_development_dependency "webmock"
-  spec.add_development_dependency "jekyll", ">= 2.0"
 end