fix(webpack-dev-server): Lock version to 3.2.1

[mattcompiles]

There is an issue with the latest version of webpack-dev-server (v3.3.1) working in sku. We should look at this issue but I think it may be on their end. Either way this PR ensures users don't upgrade and get errors.

Example error.

$ npm start

> my-app@0.1.0 start /Users/gkljajic/projects/my-app
> sku start


Starting the development server on http://localhost:8080/

ℹ ｢wdm｣: wait until bundle finished: /
🚨 HtmlRenderPlugin: An error occured rendering HTML ReferenceError: self is not defined
    at Object.eval (webpack://static/(webpack)-dev-server/client?:51:19)
    at eval (webpack://static/(webpack)-dev-server/client?:299:30)
    at Object../node_modules/webpack-dev-server/client/index.js?http://localhost (render.js:2532:1)
    at __webpack_require__ (render.js:30:30)
    at eval (webpack://static/multi_(webpack)-dev-server/client?:1:1)
    at Object.0 (render.js:2624:1)
    at __webpack_require__ (render.js:30:30)
    at render.js:94:18
    at render.js:97:10
    at webpackUniversalModuleDefinition (render.js:3:20)
✖ ｢wdm｣: Child client:

    ERROR in html-render-webpack-plugin: An error occured during render:
    ReferenceError: self is not defined
ℹ ｢wdm｣: Failed to compile.