Fix the `self` is undefined error on `FilterHTML.js:669:22`.

[Chee7ah]

A reference to self was added in v0.6 to FilterHTML.js.

This variable is not defined in the JS version, though it is in the Python version. Presumably an accidental copy/paste error.

This PR is updating that reference to this, which it seems like it should be based on the code around it.