Rely on rubocop-jekyll (#62)

Merge pull request 62

Author: DirtyF

.rubocop.yml

@@ -1,5 +1,6 @@
+require: rubocop-jekyll
 inherit_gem:
-  jekyll: .rubocop.yml
+  rubocop-jekyll: .rubocop.yml
 
 AllCops:
   TargetRubyVersion: 2.3

jekyll-gist.gemspec

@@ -26,6 +26,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "jekyll", ">= 3.0"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "rspec"
-  spec.add_development_dependency "rubocop", "~> 0.57.2"
+  spec.add_development_dependency "rubocop-jekyll", "~> 0.1.0"
   spec.add_development_dependency "webmock"
 end

lib/jekyll-gist/gist_tag.rb

@@ -16,26 +16,20 @@ def render(context)
         if (tag_contents = determine_arguments(@markup.strip))
           gist_id = tag_contents[0]
           filename = tag_contents[1]
-          if context_contains_key?(context, gist_id)
-            gist_id = context[gist_id]
-          end
-          if context_contains_key?(context, filename)
-            filename = context[filename]
-          end
+          gist_id = context[gist_id] if context_contains_key?(context, gist_id)
+          filename = context[filename] if context_contains_key?(context, filename)
           noscript_tag = gist_noscript_tag(gist_id, filename)
           script_tag = gist_script_tag(gist_id, filename)
           "#{noscript_tag}#{script_tag}"
         else
           raise ArgumentError, <<~ERROR
-          Syntax error in tag 'gist' while parsing the following markup:
-
-          #{@markup}
-
-          Valid syntax:
-            {% gist user/1234567 %}
-            {% gist user/1234567 foo.js %}
-            {% gist 28949e1d5ee2273f9fd3 %}
-            {% gist 28949e1d5ee2273f9fd3 best.md %}
+            Syntax error in tag 'gist' while parsing the following markup:
+             #{@markup}
+             Valid syntax:
+              {% gist user/1234567 %}
+              {% gist user/1234567 foo.js %}
+              {% gist 28949e1d5ee2273f9fd3 %}
+              {% gist 28949e1d5ee2273f9fd3 best.md %}
 
           ERROR
         end
@@ -48,8 +42,6 @@ def determine_arguments(input)
         [matched[1].strip, matched[2].strip] if matched && matched.length >= 3
       end
 
-      private
-
       def context_contains_key?(context, key)
         if context.respond_to?(:has_key?)
           context.has_key?(key)
@@ -90,8 +82,8 @@ def fetch_raw_code(gist_id, filename = nil)
         url = "#{url}/#{filename}" unless filename.to_s.empty?
         uri = URI(url)
         Net::HTTP.start(uri.host, uri.port,
-          :use_ssl => uri.scheme == "https",
-          :read_timeout => 3, :open_timeout => 3) do |http|
+                        :use_ssl => uri.scheme == "https",
+                        :read_timeout => 3, :open_timeout => 3) do |http|
           request = Net::HTTP::Get.new uri.to_s
           response = http.request(request)
           response.body
@@ -100,8 +92,6 @@ def fetch_raw_code(gist_id, filename = nil)
         nil
       end
 
-      private
-
       def code_from_api(gist_id, filename = nil)
         gist = GistTag.client.gist gist_id