add __esModule: true when exports

[doxiaodong]

When I use import * as classnames from 'classnames' and babel, And it throw classnames is not a function.

since babel _interopRequireWildcard doesn't do the right copy to the new newObj
when the module.exports is a function

and classnames is actually a function exports

see babel/babel#3956
and https://github.com/babel/babel/blob/master/packages/babel-helpers/src/helpers.js#L544

[doxiaodong]

By the way, the reason I use import * as classnames from 'classnames' rather than default import is https://github.com/mradamczyk/DefinitelyTyped/blob/fae50ad424116d7179e9e9d20651ba17ad229d84/types/classnames/index.d.ts#L24

[dcousens]

See #150 (preferred)