Fix server_test compile error

psiphon/server/server_test.go

@@ -51,7 +51,7 @@ func TestMain(m *testing.M) {
 	var err error
 	for _, interfaceName := range []string{"eth0", "en0"} {
 		var serverIPv4Address, serverIPv6Address net.IP
-		serverIPv4Address, serverIPv6Address, err = common.GetInterfaceIPAddress(interfaceName)
+		serverIPv4Address, serverIPv6Address, err = common.GetInterfaceIPAddresses(interfaceName)
 		if err == nil {
 			if serverIPv4Address != nil {
 				serverIPAddress = serverIPv4Address.String()