package/libcurl: security bump to version 7.64.0

package/libcurl: security bump to version 7.64.0

Fixes the following security issues:

CVE-2018-16890: NTLM type-2 out-of-bounds buffer read
https://curl.haxx.se/docs/CVE-2018-16890.html

CVE-2019-3822: NTLMv2 type-3 header stack buffer overflow
https://curl.haxx.se/docs/CVE-2019-3822.html

CVE-2019-3823: SMTP end-of-response out-of-bounds read
https://curl.haxx.se/docs/CVE-2019-3823.html

The copyright year changed in the COPYING file, so update the hash.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>