gnuplot: bump to version 4.6.6

Also add hash file.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/gnuplot/gnuplot.hash

@@ -0,0 +1,3 @@
+# From http://sourceforge.net/projects/gnuplot/files/gnuplot/4.6.6/
+md5	9c541f553c2491c56fc8b6126ff4ff73	gnuplot-4.6.6.tar.gz
+sha1	53802f565a87a6d5044d0b9c2422b5eb905d1d45	gnuplot-4.6.6.tar.gz

package/gnuplot/gnuplot.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-GNUPLOT_VERSION = 4.6.2
+GNUPLOT_VERSION = 4.6.6
 GNUPLOT_SITE = http://downloads.sourceforge.net/project/gnuplot/gnuplot/$(GNUPLOT_VERSION)
 GNUPLOT_LICENSE = gnuplot license (open source)
 GNUPLOT_LICENSE_FILES = Copyright