Enforce is-plain-object

[etpinard]

Lib.isPlainObject fails in our imagetest docker image test container at the moment.

More specifically,

Object.getPrototypeOf(obj) === Object.prototype

is false for plain objects in imagetest. This behaviour is due to how the async utility lash applies functions to objects. Making a fix lash and/or the imagetest would have been arduous, so I decided to patch Lib.isPlainObject instead.

The patch in c09cbb3 makes Lib.isPlainObject only check for

Object.prototype.toString.call(obj) === '[object Object]'

in nw.js environments. This lead to

function A() {}

Lib.isPlainObject(new A());

to return true. I'd argue that this is fine in imagetest where request bodies are JSON stringified and JSON parsed before plotting - note that JSON.parse(JSON.stringify(new A()) returns {}.

Commit e1f6818 enforces Lib.isPlainObject is the source files.