Fix language matching in code directive

Request Type: docs

How to reproduce: 

Component(s): misc core

Impact: small

Complexity: small

This issue is related to: 

**Detailed Description:**

The language matching for the `code` directive in docs app is not working.

For example, `class="lang-javascript"` should match `javascript` but it doesn't

**Other Comments:**

Includes:

* Fix for the `code` directive
* Tests for the `code` directive