[rich-text-editor] Add a smoke-test to check for minified Quill

[web-padawan]

The original change to make Quill work with webpack was done at vaadin/vaadin-rich-text-editor@88ae284.

Every time we re-build Quill from the fork, it needs to be done again. I forgot to do it for 1.2.1.
This was fixed by vaadin/vaadin-rich-text-editor@63d0636 and released as 1.2.2

We should have some kind of smoke test preventing this from happening.