git: openjdk/jfx: 8231590: Update location of jfx repo to GitHub in third-party legal files

[duke]

Changeset: 0a0d34a0
Author:    Kevin Rushforth <kcr at openjdk.org>
Date:      2019-10-03 21:48:44 +0000
URL:       https://git.openjdk.java.net/jfx/commit/0a0d34a0

8231590: Update location of jfx repo to GitHub in third-party legal files

Reviewed-by: almatvee

! modules/javafx.media/src/main/legal/glib.md
! modules/javafx.media/src/main/legal/gstreamer.md
! modules/javafx.web/src/main/legal/webkit.md