Fix set iterableToString test on IE11

[lucasfcosta]

Purpose (TL;DR)

This fixes the failing tests on IE11 introduced in #1215 .

Background

Our implementation of typeOf was too simple and didn't handle older implementations of Maps and Sets.

Even with the if clauses guarding the Map and Set related tests they would fail, because IE11 did implement them, however, IE11's implementation wasn't following the ECMA standard. This caused our type detection to fail without recognizing these object's types correctly.

Also, IE11's Set constructor was a bit weird and didn't accept an array of elements as argument, so I had to use multiple .add calls to add elements to a Set.

Solution

I added type-detect to solve the typeOf related problem.

I'm not sure everyone agrees on that. So, if you don't want that please let me know and I'll dedicate more time to rewrite typeOf and make it compatible with older browsers implementations of Maps and Sets. However, this library is maintained by everyone at Chai and other awesome contributors and it's pretty stable and has good performance.

IMO, having less code to maintain is always good and maybe we can join efforts on that library making it better for everyone.

I have also changed the Set constructor on a test in order to use an IE11 compliant way of creating Sets.

How to verify - mandatory

1. Check out this branch (see github instructions below)
2. npm install
3. npm run test

Let me know if you disagree with anything and I'll happily fix it.

PS.: Sorry for breaking your build! 😅

[coveralls]

Coverage decreased (-0.04%) to 95.407% when pulling a1b3693 on lucasfcosta:fix-set-iterableToString-ie11 into 3500d60 on sinonjs:master.

[fatso83]

I had no idea that the typeOf code was that simple. I have no objections to this, as it seems like a very minor thing.

[fatso83]

Great PR descriptons btw! Making the life of maintainers much easier.