Fix Webpack v3.4.0 compatibility issue

[logicalicy]

Summary

Chunk.entry has been deprecated and any attempt at accessing it throws an error.

This fixes an issue found while creating a bundle with Webpack v3.4.0:

ERROR in chunk vendor [entry]
js/vendor.[hash].js
Chunk.entry was removed. Use hasRuntime()

Among other issues that may be related to this issue: #43, #45.

[lostthetrail]

@logicalicy +1
@diurnalist Can we get this reviewed and potentially patched?

[diurnalist]

Thanks for the patch. We merged #44, which solves the same problem.