hg: openjfx/jfx-dev/rt: 8210508: Update JDK_DOCS property to point to JDK 12 docs

[kevin.rushforth at oracle.com]

Changeset: e64f75359064
Author:    kcr
Date:      2019-03-26 04:38 -0700
URL:       http://hg.openjdk.java.net/openjfx/jfx-dev/rt/rev/e64f75359064

8210508: Update JDK_DOCS property to point to JDK 12 docs
Reviewed-by: prr, arajkumar

! build.gradle