Need to update node-sass to sass and update image-webpack-loader

[richhauck]

Had difficulty publishing as node-sass is now deprecated. Installing sass and modifying config/webpack.loaders.js L76 to:
implementation: require("sass"), resolved this for me.

Also, wouldn't build when I had an image in the images folder as it threw the following error:

    ERROR in ./images/lights.jpg
    Module build failed (from ../node_modules/image-webpack-loader/index.js):
    Error: spawn /static-site-boilerplate/node_modules/mozjpeg/vendor/cjpeg ENOENT
        at Process.ChildProcess._handle.onexit (internal/child_process.js:269:19)
        at onErrorNT (internal/child_process.js:465:16)
        at processTicksAndRejections (internal/process/task_queues.js:80:21)
     @ ./index.html (../node_modules/html-webpack-plugin/lib/loader.js!./index.html) 1:241-271

Upgrading to "image-webpack-loader": "^7.0.1", fixed this for me.