Thrift-4647: Node.js Filesever webroot fixed path

Updates the node.js fileserver to have a fixed based webroot which can
not be escaped by end users.
diff --git a/lib/js/test/server_https.js b/lib/js/test/server_https.js
index 504f3b5..1a171dd 100644
--- a/lib/js/test/server_https.js
+++ b/lib/js/test/server_https.js
@@ -42,7 +42,7 @@
 };
 
 const ThriftWebServerOptions = {
-  files: '.',
+  files: __dirname,
   tls: {
      key: fs.readFileSync('../../../test/keys/server.key'),
      cert: fs.readFileSync('../../../test/keys/server.crt')