fix(loader): use isPlainObject when merging.

[lholmquist]

Earlier this week, one of my modules, the openshift-rest-client, which is built on top of the kubernetes-client, started to break when uploading a binary file. Basically, we create a readStream from a local file using fs.createReadStream which gets added to the request body

The error was happening in the Request module, at the point where it looks to set the ContentLength, which is should skip over if the body is a stream. Code link for reference: https://github.com/request/request/blob/3c0cddc7c8eb60b470e9519da85896ed7ee0081e/request.js#L441

The problem started happening when we upgraded to [email protected], and after some digging i noticed that the merge libraries where swapped. Since deepmerge by default clones every object property, it was "stripping" the fact that the object i passed in was a ReadStream

according to the docs, https://www.npmjs.com/package/deepmerge#ismergeableobject , that can be fixed using the "isPlainObject" module when doing merges.

This PR adds the isPlainObject module and also adds that third parameter to the merge function calls.

I create a repo where i was basically simulating what was happening to show the difference: https://github.com/lholmquist/merge-deep-merge-fu

[silasbw]

Thanks for the fix. Sorry about that.