tls: Add support for the tls-alpn-01 challenge (#2201)

* tls: Add support for the tls-alpn-01 challenge

Also updates lego/acme to latest on master.

TODO: This implementation of the tls-alpn challenge is not yet solvable
in a distributed Caddy cluster like the http challenge is.

* build: Allow building with the race detector

* tls: Support distributed solving of the TLS-ALPN-01 challenge

* Update vendor and add a todo in MITM checker

caddyhttp/httpserver/https.go

@@ -207,7 +207,7 @@ func redirPlaintextHost(cfg *SiteConfig) *SiteConfig {
 		Addr:       Address{Original: addr, Host: host, Port: port},
 		ListenHost: cfg.ListenHost,
 		middleware: []Middleware{redirMiddleware},
-		TLS:        &caddytls.Config{AltHTTPPort: cfg.TLS.AltHTTPPort, AltTLSSNIPort: cfg.TLS.AltTLSSNIPort},
+		TLS:        &caddytls.Config{AltHTTPPort: cfg.TLS.AltHTTPPort, AltTLSALPNPort: cfg.TLS.AltTLSALPNPort},
 		Timeouts:   cfg.Timeouts,
 	}
 }