.github: use HTTPS for Stack Overflow link in SUPPORT.md
.github: use HTTPS for Stack Overflow link in SUPPORT.md

Change-Id: I4e339b7c359a7cdb0933f7624ce190086c9c3599
Reviewed-on: https://go-review.googlesource.com/118155
Reviewed-by: Tobias Klauser <0a68dd4915066ec5d3f81f75a828fee53dcc8822@gmail.com>

CAFxX/go,CAFxX/go,akutz/go,nawawi/go,nawawi/go,akutz/go,akutz/go,golang/go,akutz/go,CAFxX/go,nawawi/go,golang/go,golang/go,akutz/go,josharian/go,josharian/go,CAFxX/go,akutz/go,nawawi/go,CAFxX/go,golang/go,cloudflare/go,golang/go,nawawi/go,josharian/go,josharian/go,nawawi/go,akutz/go,cloudflare/go,josharian/go,CAFxX/go,josharian/go,golang/go,cloudflare/go,josharian/go,cloudflare/go,cloudflare/go,golang/go,cloudflare/go,golang/go,akutz/go,cloudflare/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,josharian/go,CAFxX/go