libcurl: security bump to version 7.59.0

libcurl: security bump to version 7.59.0

CVE-2018-1000120: curl could be fooled into writing a zero byte out of
bounds when curl is told to work on an FTP URL with the setting to only
issue a single CWD command, if the directory part of the URL contains a
"%00" sequence.

https://curl.haxx.se/docs/adv_2018-9cd6.html

CVE-2018-1000121: curl might dereference a near-NULL address when
getting an LDAP URL.

https://curl.haxx.se/docs/adv_2018-97a2.html

CVE-2018-1000122: When asked to transfer an RTSP URL, curl could
calculate a wrong data length to copy from the read buffer.

https://curl.haxx.se/docs/adv_2018-b047.html

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>