Add stats for query and cache requests

[GKosheev]

Issue #64

I implemented get method to get the size of cached calls:

get numberOfCachedCalls() {
    return this._cache.size
}

[szmarczak]

This is actually incorrect. It doesn't return the total number of cached requests, but the current cache size. I'd implement it like this:

this.stats = {
	cache: 0,
	query: 0,
};

and increment the counters respectively in

cacheable-lookup/source/index.js

Line 213 in 5b08a36

async query(hostname) {

You also need to provide some tests.

[szmarczak]

@GKosheev No need to duplicate code in the comments :) There's a review feature and you can add comments there if necessary.

[GKosheev]

I'm not sure if I did the unit test as you wanted me to, I tried to follow the example you sent me with the verify method.
But I am always ready to make corrections.

[GKosheev]

@szmarczak, should I change something specific in the last commit?

[GKosheev]

@szmarczak, would that work?

[szmarczak]

Will take a look now, sorry for delay. Also, no need to post a comment of your commit changes :)

[szmarczak]

Looks good! Thanks for contributing! ❤️