Validate whether CopyPattern jsdoc is up to date

We upgraded the copy plugin we bundle with these helpers, but I forgot to validate in 0.10 whether the JSDoc type I wrote to represent the structure of a copy configuration object is still accurate. This definition (in plugins.js) should be audited to make sure it conforms to the latest API for the [copy-webpack-plugin](https://webpack.js.org/plugins/copy-webpack-plugin/)