In Production tests are not passing

# Problem - by testing Container and Nodes are not rendered
In distribution(package) mode same test not producing same snapshots results like running from package code mode - please compare snapshots - by importing SortableTree from npm package and running tests missing complete ReactVirtualized__Grid__innerScrollContainer (no nodes are rendered)

Please make new app with cra and add packages from given test and run it.
```javascript
import React from 'react'
import renderer from 'react-test-renderer'
import Enzyme from 'enzyme'
import Adapter from 'enzyme-adapter-react-16'
import SortableTree from 'react-sortable-tree'

Enzyme.configure({ adapter: new Adapter() })

describe('', () => {
it('should render tree correctly', () => {
const tree = renderer
.create( {} } />, {
createNodeMock: () => ({}),
})
.toJSON()

expect(tree).toMatchSnapshot()
})
})
```

also run same test in src folder and compare results.

Create the CRA reproduction described in the issue and run the provided SortableTree snapshot test using the npm package. Run the same test from the src folder, compare the snapshots, and verify that the production-package result renders the expected ReactVirtualized grid container and tree nodes.

Written by the indexing model from the issue text.