bump jupyterlab to 0.34.9

needed for Python 3.7 because 0.34.0 hasn't been packaged for 3.7

repo2docker/buildpacks/conda/environment.yml

@@ -1,7 +1,7 @@
 dependencies:
   - python=3.6.*
   - ipywidgets==7.2.1
-  - jupyterlab==0.34.0
+  - jupyterlab==0.34.9
   - tornado==4.5.3
   - notebook==5.6.0
   - pip: