Decorators with transform-decorators-legacy

Hello,

I've been using [transform-decorators-legacy](https://github.com/loganfsmyth/babel-plugin-transform-decorators-legacy) until the decorator spec is approved. It works fine when building, but the plugin doesn't seem to run when babel is executed through documentation.js

My .babelrc is:

``` json
{
"presets": ["react", "es2015", "stage-0"],
"plugins": ["transform-decorators-legacy"]
}
```

Using documetation `4.0.0-beta2` and babel `6.7.7`

The error: `Decorators are not supported yet in 6.x pending proposal update`, is the same error you would get if you try to build without the `transform-decorators-legacy` plugin

I see in #367 that other plugins seem to run, so not quite sure what's going wrong here.