Support functions in plugins array

[jdalton]

Newer versions of '@rollup/plugin-node-resolve' don't export a traditional default module.exports = pluginFunc any more so the pattern of require(pluginId) doesn't work. Instead it has a .default property on its export. It would be nice to be able to support plugins like '@rollup/plugin-node-resolve' without resorting to a custom plugin wrapper. Maybe it could be solved by allowing a function to be passed:

import { nodeResolve } from '@rollup/plugin-node-resolve'
// ...
plugins: [nodeResolve]

or by checking for the .default property but that might be brittle. Maybe:

let plugin = require(id);
if (typeof plugin !== 'function' && typeof plugin.default === 'function') {
  plugin = plugin.default;
}