Replacing 'HTTP' by 'HTTPS' for securing links (#3682)

Currently, when we access github.com with HTTP, it is redirected to HTTPS automatically. So this commit aims to replace http://github.com by https://github.com for security.
Signed-off-by: Kim Bao Long <longkb@vn.fujitsu.com>

plugin/pkg/fall/fall.go

@@ -7,7 +7,7 @@
 //
 // The take away: be mindful of this and don't blindly assume it's a good feature to have in your plugin.
 //
-// See http://github.com/coredns/coredns/issues/2723 for some discussion on this, which includes this quote:
+// See https://github.com/coredns/coredns/issues/2723 for some discussion on this, which includes this quote:
 //
 // TL;DR: `fallthrough` is indeed risky and hackish, but still a good feature of CoreDNS as it allows to quickly answer boring edge cases.
 //