package/gsl: bump to version 2.8

Release notes:
https://cgit.git.savannah.gnu.org/cgit/gsl.git/tree/NEWS?h=release-2-8

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

package/gsl/gsl.hash

@@ -1,3 +1,3 @@
 # Locally calculated after checking pgp signature
-sha256  dcb0fbd43048832b757ff9942691a8dd70026d5da0ff85601e52687f6deeb34b  gsl-2.7.1.tar.gz
+sha256  6a99eeed15632c6354895b1dd542ed5a855c0f15d9ad1326c6fe2b2c9e423190  gsl-2.8.tar.gz
 sha256  8ceb4b9ee5adedde47b31e975c1d90c73ad27b6b165a1dcd80c7c545eb65b903  COPYING

package/gsl/gsl.mk

@@ -4,7 +4,7 @@
 #
 ################################################################################
 
-GSL_VERSION = 2.7.1
+GSL_VERSION = 2.8
 GSL_SITE = $(BR2_GNU_MIRROR)/gsl
 GSL_INSTALL_STAGING = YES
 GSL_LICENSE = GPL-3.0