Enable babelrc plugins with options array syntax

[jakubrohleder]

Recently I've been fiddling a lot with multiple approaches to styles. By accident I've discovered a small bug that this pull request is fixing.

Babel docs allows two type of plugin syntax: string or an array with options e.g.

{
  "plugins": [
    "add-module-exports",
    ["css-in-js", { "vendorPrefixes": true, "bundleFile": "public/bundle.css" }]
  ]
}

The second syntax caused an error, as normalization casts array to string.

[KyleAMathews]

console.log slipped in

[jakubrohleder]

my bad :)

[KyleAMathews]

LGTM, @benstepp?

[benstepp]

👍

Now that I'm looking at the whole range of options Babel let's you use, we should probably Object.assign the normalized plugins/presets with the user's .babelrc rather than just creating a new object.

[KyleAMathews]

@jakubrohleder what do you think about @benstepp's idea?

[jakubrohleder]

@KyleAMathews Sorry for late response I've had quite a busy weekend. I completely agree with @benstepp idea of using Object.assign(), but as far as I see it is already implemented in #294

[benstepp]

Yeah I needed it when supporting cacheDirectory. This PR looks great now.

[KyleAMathews]

@jakubrohleder I'll still merge this PR then Ben's over it so you get the commit credit as this was your initiative after all. And no worries about the slow reply! We're all volunteers here :-) Thanks!

[KyleAMathews]

@jakubrohleder @benstepp so... I might of merged things together wrong. I removed the

if (isArray(plugin)) {
  normalizedPlugin = [resolvePlugin(plugin[0], directory, 'plugin'), plugin[1]]
} else {
  normalizedPlugin = resolvePlugin(plugin, directory, 'plugin')
}

stuff when merging in Ben's object-assign addition but now the babel config tests broke. Was I supposed to have left the above code in?

[benstepp]

Leave the above in (also the lodash import). It's the change that support the babel plugin configs.

npm run test of the current master 6d79282 still pass for me.

[KyleAMathews]

Ok, thanks. Restored these changes in f77efe6