allow host without port passed as 'host' argument in Dial function.

Previously, if the given host doesn't contain port, dial with it will
result in error "missing port in address".

client.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"strings"
 	"sync"
 
 	"github.com/lucas-clemente/quic-go/internal/handshake"
@@ -151,11 +152,16 @@ func newClient(
 		tlsConf = &tls.Config{}
 	}
 	if tlsConf.ServerName == "" {
-		var err error
-		tlsConf.ServerName, _, err = net.SplitHostPort(host)
-		if err != nil {
-			return nil, err
+		sni := host
+		if strings.IndexByte(sni, ':') != -1 {
+			var err error
+			sni, _, err = net.SplitHostPort(sni)
+			if err != nil {
+				return nil, err
+			}
 		}
+
+		tlsConf.ServerName = sni
 	}
 
 	// check that all versions are actually supported