gnutls: bump to version 3.2.18

Also add hash, calculated on downloaded file after verifying signature.

[Peter: tweak hash comment]
Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gnutls/gnutls.hash

@@ -0,0 +1,2 @@
+# Locally calculated after checking pgp signature
+sha256	4762afab5e1b9e829c5f53d2b00cd5e41d43fa6d035efcf239e3fe0459134d45	gnutls-3.2.18.tar.xz

package/gnutls/gnutls.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 GNUTLS_VERSION_MAJOR = 3.2
-GNUTLS_VERSION = $(GNUTLS_VERSION_MAJOR).16
+GNUTLS_VERSION = $(GNUTLS_VERSION_MAJOR).18
 GNUTLS_SOURCE = gnutls-$(GNUTLS_VERSION).tar.xz
 GNUTLS_SITE = ftp://ftp.gnutls.org/gcrypt/gnutls/v$(GNUTLS_VERSION_MAJOR)
 GNUTLS_LICENSE = GPLv3+ LGPLv2.1+