Fix wrong parameter type in cache.php

[mentosmenno2]

Issue link

Description

Fixes issue where plugins are old-scool, and pass id's as strings.
Which would crash, because we require an integer.

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.