build: update curl submodule to 7.66.0

The submodule was on 7.65.3 version. This update closes two security
problems:

https://curl.haxx.se/docs/CVE-2019-5482.html
https://curl.haxx.se/docs/CVE-2019-5481.html

See also curl-7.66.0 release notes:

https://curl.haxx.se/changes.html#7_66_0

Fixes #4502.

(cherry picked from commit 4c2d1eff)

curl @ 9cd755e1

-Subproject commit aa73eb47bc8583070734696b25b34ad54c2c1f5e
+Subproject commit 9cd755e1d768bbf228e7c9faf223b7459f7e0105