PARTIAL: Update to jupyter-lab 1.0.

[idvorkin]

I'm not too familiar with jupyter lab extensions, and won't have time to dig in for a bit. This change is NOT complete. It builds but doesn't work. Posting it in hopes it inspires others ;)

The plugin executes and throws an exception here:

codemirror.js:7726 Uncaught (in promise) TypeError: Cannot read property 'attach' of undefined
    at CodeMirror.<anonymous> (codemirror.js:7726)
    at codemirror.js:3908
    at CodeMirror.setOption (codemirror.js:8219)
    at Object.setOption (editor.js:1097)
    at CodeMirrorEditor.setOption (editor.js:246)
    at VimCell.push.vDQl.VimCell._onActiveCellChanged (index.js:35)
    at new VimCell (index.js:24)
    at index.js:

Please finish the following when submitting a pull request:

• [X] Add a line to History.md briefly documenting the change.

If this is a release, additionally do the following:

• [X] Bump the package version in package.json
• [X] Update the dependencies in package.json
• [ ] Run jlpm install to update yarn.lock

Thanks!

[jwkvam]

Thanks for the effort, I really do appreciate it, it makes maintaining this much easier for me :)

Sorry I got here late, I merged #89 instead.