bugfix: don't error in css_classes

lib/banzai/filter/syntax_highlight_filter.rb

@@ -19,8 +19,15 @@ module Banzai
         language = node.attr('class')
         code     = node.text
 
+        lexer = Rouge::Lexer.find_fancy(language)
+        formatter = Rouge::Formatters::HTML.new
+        css_classes = "code highlight js-syntax-highlight #{lexer.tag}"
+
         begin
-          highlighted = %<<pre class="#{css_classes}"><code>#{block_code(code, language)}</code></pre>>
+          highlighted = ''
+          highlighted << %<<pre class="#{css_classes}"><code>>
+          highlighted << formatter.format(lexer.lex(code))
+          highlighted << %<</code></pre>>
         rescue
           # Gracefully handle syntax highlighter bugs/errors to ensure
           # users can still access an issue/comment/etc.
@@ -31,10 +38,6 @@ module Banzai
         replace_parent_pre_element(node, highlighted)
       end
 
-      def css_classes
-        "code highlight js-syntax-highlight #{lexer.tag}"
-      end
-
       private
 
       def replace_parent_pre_element(node, highlighted)