Tailwind content parsing breaks the module

[kpdemetriou]

Steps to reproduce

Set content in tailwind.config.js to a non-array as described in the Tailwind docs.

What is Expected?

The absence of errors.

What is actually happening?

Cannot start nuxt: (tailwindConfig.content || []).map is not a function.

Additional Commentary

You cannot assume that tailwindConfig.content is an array. It can also be an object. In the event that tailwindConfig.content is an object, you want to derive the list of files from tailwindConfig.content.files.

[ineshbose]

Let's track this in #671