contrib: gcrypt: switch URL to HTTPS

This avoids a redirection. It was also the only gnupg.org URL which didn't use HTTPS already.

contrib/src/gcrypt/rules.mak

 # GCRYPT
 GCRYPT_VERSION := 1.10.1
-GCRYPT_URL := http://www.gnupg.org/ftp/gcrypt/libgcrypt/libgcrypt-$(GCRYPT_VERSION).tar.bz2
+GCRYPT_URL := https://www.gnupg.org/ftp/gcrypt/libgcrypt/libgcrypt-$(GCRYPT_VERSION).tar.bz2
 
 PKGS += gcrypt
 ifeq ($(call need_pkg,"libgcrypt"),)