For release note, see:
http://www.gnuplot.info/ReleaseNotes_6_0_3.html
SHA256 hash now from:
https://sourceforge.net/projects/gnuplot/files/gnuplot/6.0.3/gnuplot-6.0.3.tar.gz.sha256
Signed-off-by: Michael Fischer <mf@go-sys.de>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 7443e881f8)
Signed-off-by: Titouan Christophe <titouan.christophe@mind.be>