Fix ublock spelling (#308)
Fix ublock spelling (#308)

* Fix ublock spelling

* Rename "add-on" to "extension"

Not that it's a major issue, but Google Chrome calls them extensions, and Firefox calls them add-ons.

fastai/course-v3,fastai/course-v3,fastai/course-v3,fastai/course-v3,fastai/course-v3,fastai/course-v3,fastai/course-v3