fix(heap): this is undefined

[ojj1123]

What's the problem?

• MaxHeapAdhoc and MinHeapAdhoc constructor can get an array for filling the heap initially.
• And then the constructors execute this:

this.heap.forEach(this.add);

• But It did occur this error:
  

• The problem is that if passing this.add method literally, this used by add method is undefined.

• This issue is confusing for the developers. And your intend is that MaxHeapAdhoc and MinHeapAdhoc is used by developers easily

#1117

This PR contains several minimalistic (by their functionalities and implementation) data structures like MinHeap, MaxHeap, and DisjointSet that don't have external dependencies and that are easy to copy-paste and use during the coding interview if allowed by the interviewer.

How to fix

• Just use arrow function

this.heap.forEach((value) => this.add(value));

[ojj1123]

@trekhleb
I was wondering if you could review this PR!
I think it is important since your intend could be broken up.