Deletion of .mdx files under folders doesn't trigger webpack compilation

[fmal]

To reproduce add some pages in the root pages folder and nest some pages under a folder. Deleting root pages results in Webpack recompilation and nav tree updated, but if you delete a page under folder there is no update.
Seems like the fix is to add addContextDependency not only for pages but every child directory within it as well (ideally using a glob like pages/**).

[dimaMachina]

On 2.0.0-beta.10 I removed a MDX file and hot reload worked