Fix: Stale cache path

When determining the stale cache path, all instances of 'html' where being replaced with 'stale.html'. This caused problems if the path contained folders with html in their name.

Example: /public_html/ became /public_stale.html/
Merge pull request #1 from jonom/patch-1

Fix: Stale cache path
Merge pull request #12 from jonom/master

Fix: Stale cache path