Using hasOwnProperty breaks for config objects with null prototype

[cspotcode]

I'm loading a config object from a third-party library, then passing it to yargs. This library happens to return an object with a null prototype. yargs breaks because it's trying to call config.hasOwnProperty.

https://github.com/yargs/yargs/blob/master/lib/apply-extends.js#L22

[bcoe]

@cspotcode any chance you could provide a minimal reproduction of the issue?

[cspotcode]

https://runkit.com/5d12741cd8940e00146b7254/5d24bb163b4b940013e6d846

In my case the config object is coming from another library which is doing the right thing: it's returning an object with a null prototype, which is generally easier to work with as a dictionary. That's all correct and good. yargs just needs a tiny patch to fix how it's using hasOwnProperty.