Update sym-link in release notes for JavaFX 11

Now that the OpenJFX community site is live at https://openjfx.io/ we should update the following link in the release notes to point to it:

Old:
[Getting Started with JavaFX 11](http://docs.gluonhq.com/javafx11/index.html#introduction)

New:
[Getting Started with JavaFX 11](https://openjfx.io/openjfx-docs/)