Bump jupyterlab and dask-labextension to 2.x

[jrbourbeau]

This PR bumps both Jupyterlab and dask-labextension to their latest releases (2.0.0).

[jrbourbeau]

As a side note, I'm getting the following error when binder attempts to build the dask-tutorial environment:

Step 51/56 : RUN ./binder/postBuild
 ---> Running in 30ebb797e2dc
Building jupyterlab assets (build:prod:minimize)
The extension "jupyter-offlinenotebook" is outdated.

Building jupyterlab assets (build:prod:minimize)
The extension "jupyter-offlinenotebook" is outdated.

An error occured.
ValueError: This extension does not yet support the current version of JupyterLab.

Conflicting Dependencies:
JupyterLab                        Extension      Package
>=2.0.0 <2.1.0                    >=1.1.3 <2.0.0 @jupyterlab/application
>=2.0.0 <2.1.0                    >=1.1.3 <2.0.0 @jupyterlab/apputils
>=2.0.0 <2.1.0                    >=1.1.3 <2.0.0 @jupyterlab/notebook
>=2.0.0 <2.1.0                    >=1.4.0 <2.0.0 @jupyterlab/rendermime-interfaces
>=5.0.0 <5.1.0                    >=4.1.1 <5.0.0 @jupyterlab/services
See the log file for details:  /tmp/jupyterlab-debug-4vujyphr.log
Removing intermediate container 30ebb797e2dc
The command '/bin/sh -c ./binder/postBuild' returned a non-zero code: 1

I'm hoping that updating the jupyterlab + dask extension versions will help resolve the build issue.

Either way, I think we should update to 2.0 here

EDIT:

Actually it looks like the build issue is with the jupyter-offlinenotebook package

[TomAugspurger]

@jrbourbeau your recommendation is to merge this now, or to pin those to 1.x until all the extensions are compatible?

[jrbourbeau]

Sorry I did more investigating on JupyterLab 2.0 compatibility but forgot to comment here about it. We should hold off on merging this PR and instead pin to 1.x until extensions are updated (e.g. https://github.com/manics/jupyter-offlinenotebook/issues/28). I'll open a PR to do the 1.x pinning