Update transformation: outputPath

[bitpshr]

Do you want to request a feature or report a bug?
Feature

What is the current behavior?
The current transformation supports migrating a webpack configuration from v1 to v2.

What is the expected behavior?
The transformation should support migrating a webpack configuration from v3 to v4.

If this is a feature request, what is motivation or use case for changing the behavior?
After some discussion the decision was made to update our migration transformations to actively support migrating only from the previous version to the current version, which currently means v3 - v4. Migrating older versions such as v1 or v2 will no longer be supported.

This feature request is to update the outputPath transformation accordingly.

[matheus1lva]

Not needed anymore, webpack expects/allows it to be an string as seemed here.