notifications: configure cleanup, update libwebsockets

Version of libwebsockets is now set to
https://github.com/cejkato2/libwebsockets
(HEAD)

Installation of libwebsockets (with respect to its README), tested on
redhat-based distro:
mkdir build; cd build; cmake ..&& make libwebsockets_rpm
yum install ./RPM/RPMS/x86_64/*
diff --git a/src/notification-server.c b/src/notification-server.c
index 151d1b5..b58bd3d 100644
--- a/src/notification-server.c
+++ b/src/notification-server.c
@@ -133,7 +133,7 @@
 
 		sprintf(buf, "%s%s", resource_path, whitelist[n].urlpath);
 
-		if (libwebsockets_serve_http_file(context, wsi, buf, whitelist[n].mimetype, NULL))
+		if (libwebsockets_serve_http_file(context, wsi, buf, whitelist[n].mimetype, NULL, 0))
 			return -1; /* through completion or error, close the socket */
 
 		/*