libnss: security bump to version 3.20.1

Fixes:
CVE-2015-7181 - A use-after-poison flaw was found in the way NSS parsed
certain ASN.1 structures. An attacker could use this flaw to cause NSS
to crash or execute arbitrary code with the permissions of the user
running an application compiled against the NSS library.
CVE-2015-7182 - A heap-based buffer overflow flaw was found in the way
NSS parsed certain ASN.1 structures. An attacker could use this flaw to
cause NSS to crash or execute arbitrary code with the permissions of the
user running an application compiled against the NSS library.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>