When setting nested array paths, look for object paths not just array paths

[clayne11]

Fixes #1

[aldeed]

@clayne11 Thanks for the PR. It's possible there is something to fix here, but a position string is never supposed to have any periods in it unless they are part of the object key. So this fix doesn't seem correct.

It's done this way to support Mongo modifier objects. For example, {$set: {'a.b.c': 1}} would have a position string like $set[a.b.c]. So we never want to split on periods because they are part of the key. By contrast, the position key for {$set: {a: {b: {c: 1}}}} should be $set[a][b][c]. It's all done in bracket notation.

I might be misunderstanding what you're doing here, or maybe there is a different solution for the core problem this is fixing.

[clayne11]

The issue is that this library supports both Mongo modifier objects and plain JS objects. The fix I put in only runs on plain JS objects, not on Mongo modifier objects. The issue occurred when trying to set an array value in a plain JS object that was nested under an object key. You can see the tests I put it in that show the issue. If you run those tests without the changes I made to the code you can see how it resolved the issue.