ci: Build and test on Go 1.16, bump minimum to 1.15

[francislavoie]

🎉

[mohammed90]

The Go version in go.mod needs to be bumped up to 1.15. The commit ab80ff4 (admin: remote management) uses the PublicKey#Equal method, which was added in go1.15.

caddy/admin.go

Lines 552 to 553 in ec3ac84

	comparer, ok := peerCert.PublicKey.(interface{ Equal(crypto.PublicKey) bool })
	if !ok || !comparer.Equal(allowedKey) {

Which means we need to drop '1.14' in the CI flows as well.

[francislavoie]

Oops - @mholt you'll need to turn off the requirement in the repo settings that the test (macos-latest, 1.14) and such pass.

[mholt]

Thanks, good point. Done!

[francislavoie]

👍

I'm thinking this is good to go?