Detect and preserve npm package-lock.json file indentation

[alexanderanchishkin]

I used detect-indent package as it was used for npm install fix

[ai]

Can we avoid extra dependency and write a small function to do it? Our use case is very simple to use extra dependency for that.

[alexanderanchishkin]

Sure. I fixed it.
But I discovered interesting fact. Really npm v7+ doesn't preserve indentation style after npm install (and we use it for updating). More information about it here. It uses indentation of package.json file.
So this PR was useful only for npm version less v7.
Our team use npm v6 now so we'll find it useful.

[ai]

Thanks. Released in 1.0.6.