fix environment.yml

Author: goebbert1

environment.yml

@@ -3,11 +3,12 @@ name: jupyter-xprahtml5-proxy
 channels:
   - conda-forge
 dependencies:
-  - jupyterlab=3
+  - tornado>=6.3
+  - jupyterlab=4
   - jupyterlab_server
-  - jupyter-server-proxy>=3.1.0
+  - jupyter-server-proxy>=4.0
   - jupyter_conda
   - pip
   - pip:
-#      - xpra>=4.0.4
+#      - xpra>=5.0.0
       - -r file:requirements.txt