gnuplot: build-script reviewed, version 5.2.4 added to variants

Tools/gnuplot/5/variants

@@ -1,3 +1,4 @@
 gnuplot/4.6.3	stable
 gnuplot/5.0.0	stable
 gnuplot/5.2.0	stable
+gnuplot/5.2.4	stable

Tools/gnuplot/build

@@ -1,6 +1,8 @@
 #!/usr/bin/env modbuild
 
-SOURCE_URL="https://sourceforge.net/projects/gnuplot/files/$P/$V/$P-$V.tar.gz"
+pbuild::add_to_group 'Tools'
+pbuild::set_source_url "https://sourceforge.net/projects/gnuplot/files/$P/$V/$P-$V.tar.gz"
+pbuild::set_docfiles 'Copyright' 'ChangeLog' 'NEWS' 'README'
 
 pbuild::configure() {
 	"${MODULE_SRCDIR}"/configure \
@@ -10,8 +12,6 @@ pbuild::configure() {
 		|| exit 1
 }
 
-pbuild::add_to_group 'Tools'
-pbuild::set_docfiles 'Copyright' 'ChangeLog' 'NEWS' 'README'
 pbuild::make_all
 
 # Local Variables: