Resolve webpack warnings

[mikemfleming]

WARNING in configuration
The 'mode' option has not been set. Set 'mode' option to 'development' or 'production' to enable defaults for this environment.

WARNING in asset size limit: The following asset(s) exceed the recommended size limit (244 KiB).
This can impact web performance.
Assets:
bundle.js (457 KiB)

WARNING in entrypoint size limit: The following entrypoint(s) combined asset size exceeds the recommended limit (244 KiB). This can impact web performance.
Entrypoints:
main (457 KiB)
bundle.js

WARNING in webpack performance recommendations:
You can limit the size of your bundles by using import() or require.ensure to lazy load some parts of your application.
For more info visit https://webpack.js.org/guides/code-splitting/

[mikemfleming]

good opportunity to revisit babel config

[mikemfleming]

also good opportunity for ci