updating webpack and deleting yarn files in order to fix build scripts

[fergiemcdowall]

Hi!

When I build the repo as it is now, I get the following error:

fergus ~/repos/webpack-library-example 💥  ➜ npm run "build:browser"

> y@1.0.0 build:browser /home/fergus/repos/webpack-library-example
> webpack && cp dist/webpack-numbers.js examples/browser

/home/fergus/repos/webpack-library-example/node_modules/webpack-cli/bin/config-yargs.js:89
                                describe: optionsSchema.definitions.output.properties.path.description,

This pull request fixes the bug by bumping the Webpack version and removing the Yarn files (are the Yarn files in fact needed?)