Rubocop: Style/PerlBackrefs

- Avoid the use of Perl-style backrefs

lib/jekyll/convertible.rb

@@ -47,7 +47,7 @@ module Jekyll
                                  merged_file_read_opts(opts))
         if content =~ /\A(---\s*\n.*?\n?)^((---|\.\.\.)\s*$\n?)/m
           self.content = $POSTMATCH
-          self.data = SafeYAML.load($1)
+          self.data = SafeYAML.load(Regexp.last_match(1))
         end
       rescue SyntaxError => e
         Jekyll.logger.warn "YAML Exception reading #{File.join(base, name)}: #{e.message}"

lib/jekyll/document.rb

@@ -263,7 +263,7 @@ module Jekyll
           self.content = File.read(path, merged_file_read_opts(opts))
           if content =~ YAML_FRONT_MATTER_REGEXP
             self.content = $POSTMATCH
-            data_file = SafeYAML.load($1)
+            data_file = SafeYAML.load(Regexp.last_match(1))
             merge_data!(data_file) if data_file
           end
 

lib/jekyll/tags/highlight.rb

@@ -13,11 +13,11 @@ module Jekyll
       def initialize(tag_name, markup, tokens)
         super
         if markup.strip =~ SYNTAX
-          @lang = $1.downcase
+          @lang = Regexp.last_match(1).downcase
           @highlight_options = {}
-          if defined?($2) && $2 != ''
+          if defined?(Regexp.last_match(2)) && Regexp.last_match(2) != ''
             # Split along 3 possible forms -- key="<quoted list>", key=value, or key
-            $2.scan(/(?:\w="[^"]*"|\w=\w|\w)+/) do |opt|
+            Regexp.last_match(2).scan(/(?:\w="[^"]*"|\w=\w|\w)+/) do |opt|
               key, value = opt.split('=')
               # If a quoted list, convert to array
               if value && value.include?("\"")