Fix broken test build: htmlparser2 loads a .json file so webpack needs to use json-loader.
Fix broken test build: htmlparser2 loads a .json file so webpack needs to use json-loader.

charnpreetsingh185/jupyterlab,eskirk/jupyterlab,TypeFox/jupyterlab,eskirk/jupyterlab,charnpreetsingh185/jupyterlab,charnpreetsingh185/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,TypeFox/jupyterlab,TypeFox/jupyterlab,jupyter/jupyterlab,TypeFox/jupyterlab,jupyter/jupyterlab,jupyter/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab,eskirk/jupyterlab,TypeFox/jupyterlab,charnpreetsingh185/jupyterlab,eskirk/jupyterlab