try to fix inheritance for es6

[xaviergonz]

Fixes #15

[netlify]

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[xaviergonz]

@sisp care to give this branch a try and see if it fixes your CRA issue?

[coveralls]

Coverage decreased (-0.04%) to 89.32% when pulling 23136d0 on fix-inheritance-es6 into 1e8e3db on master.

[sisp]

When I use the ESM bundle built from this branch with my CRA example, it works (for both "target": "es5" and "target": "es6" in tsconfig.json). :-)

[sisp]

Do you think it makes sense to add a comment in the code that justifies this "hack" and references #15 for referring to the discussion about the problem? Perhaps ES5 support can be dropped at some point and the original version can be restored and until then nobody will accidentally "improve" this part of the code.

[xaviergonz]

Makes total sense, added, will release this as 0.13.1

[sisp]

Thanks a lot for your efforts! You're awesome!