pcre: change download location

The location at ftp.csx.cam.ac.uk only stores 2 latest versions of PCRE.
This results in old (2015.11 and older currently) buildroot versions
timing out on wget several times and having to retrieve the package
from sources.buildroot.org afterwards.

Signed-off-by: Oleg Kitain <okitain@ya.ru>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pcre/pcre.mk

@@ -5,7 +5,7 @@
 ################################################################################
 
 PCRE_VERSION = 8.40
-PCRE_SITE = ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre
+PCRE_SITE = https://ftp.pcre.org/pub/pcre
 PCRE_SOURCE = pcre-$(PCRE_VERSION).tar.bz2
 PCRE_LICENSE = BSD-3c
 PCRE_LICENSE_FILES = LICENCE