Release Note: GTK+ 3.20 and Later Unsupported by Swing

Due to incompatible changes in the GTK+ 3 library versions 3.20 and later,
the Swing GTK Look and Feel does not render some UI components when using this library.
Therefore Linux installations with versions of GTK+ 3.20 and above are not supported
for use by the Swing GTK Look And Feel in this release.
Affected applications on such configurations should specify the system property
-Djdk.gtk.version=2.2 to request GTK2+ based rendering instead.