Ensure no new npm modules get excluded accidentally by webpack

[DonJayamanne]

Currently webpack spits out a couple of warning messages about not being to include a few dependencies.
These have been reviewed and can be safely ignored, however we need a build step to ensure no new modules get ignored.

Here's whats generated today:

    WARNING in ./node_modules/encoding/lib/iconv-loader.js 9:12-34
    Critical dependency: the request of a dependency is an expression
     @ ./node_modules/encoding/lib/encoding.js
     @ ./node_modules/node-fetch/lib/body.js
     @ ./node_modules/node-fetch/index.js
     @ ./node_modules/@jupyterlab/services/lib/serverconnection.js
     @ ./node_modules/@jupyterlab/services/lib/index.js

    WARNING in ./node_modules/ws/lib/BufferUtil.js
    Module not found: Error: Can't resolve 'bufferutil' in '/Users/donjayamanne/.vscode-insiders/extensions/pythonVSCode/node_modules/ws/lib'
     @ ./node_modules/ws/lib/BufferUtil.js
     @ ./node_modules/ws/lib/Receiver.js
     @ ./node_modules/ws/index.js
     @ ./node_modules/@jupyterlab/services/lib/serverconnection.js
     @ ./node_modules/@jupyterlab/services/lib/index.js

    WARNING in ./node_modules/ws/lib/Validation.js
    Module not found: Error: Can't resolve 'utf-8-validate' in '/Users/donjayamanne/.vscode-insiders/extensions/pythonVSCode/node_modules/ws/lib'
     @ ./node_modules/ws/lib/Validation.js
     @ ./node_modules/ws/lib/Receiver.js
     @ ./node_modules/ws/index.js
     @ ./node_modules/@jupyterlab/services/lib/serverconnection.js
     @ ./node_modules/@jupyterlab/services/lib/index.js