hg: openjfx/11-dev/rt: 8209967: Bump minimum gradle version to 4.8 for JDK 11

[johan at lodgon.com]

Changeset: 65da2bfef459
Author:    kcr
Date:      2018-08-28 14:24 -0700
URL:       https://hg.openjdk.java.net/openjfx/11-dev/rt/rev/65da2bfef459

8209967: Bump minimum gradle version to 4.8 for JDK 11
Reviewed-by: prr, nlisker

! build.gradle