Use langPrefix from Markdown-it options instead of hardcoded value 'l…

…anguage-'

Markdown-it has an option called `langPrefix` for the same propose which defaults to `language-`.

Default `language-` prefix value follows W3C recommendation.

Highlight.js default behavior adds language to class list without any prefix (same as setting `langPrefix = ''` in md options).

index.js

@@ -49,7 +49,7 @@ function inlineCodeRenderer (tokens, idx, options) {
   }
 
   const highlighted = options.highlight(code.content, lang)
-  const cls = lang ? ` class="language-${lang}"` : ''
+  const cls = lang ? ` class="${options.langPrefix + lang}"` : ''
 
   return `<code${cls}>${highlighted}</code>`
 }