curl: update to version 7.52.1

This fixes the folowing security problems:

CVE-2016-9586: printf floating point buffer overflow
CVE-2016-9952: Win CE schannel cert wildcard matches too much
CVE-2016-9953: Win CE schannel cert name out of buffer read
CVE-2016-9594: unititialized random

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>