Fix XML brush: use the last occurrence of the tag

[merkushin]

Fixes #143

The solution was suggested in the issue.

Changes proposed in this Pull Request

• Use lastIndexOfinstead of indexOf: for some tags, it becomes vital to get the last occurrence. As we have encoded HTML entities (for example, < as <), some tags become a representation where the tag name appears a few times. For example <l> looks like <l>. And the first position of the tag name (l) is 1 which refers to the HTML entity, but we need to get the last appearance: 4.

Testing instructions

• Add a shortcode to a post:

  [code lang="XML"]
  <l name="John" />
  <t name="Doe" />
  [/code]
  

• Preview the post

Screenshot / Video

Before:

After:

[dadish]

[renatho]

Interesting issue! I checked if the code was updated with the last version of the brush, and it seems it is: https://github.com/syntaxhighlighter/brush-xml/blob/master/brush.js

It really seems an issue in that part, and I don't see a case where it could cause another issue.