axios 0.17 support & NodeJS current LTS support (8)

[soswow]

Changes required to have it working with axios 0.17, + while I was there I've bumped code to proper modern level, introduced linting, simplified some tests, etc

[nettofarah]

Hi, @soswow.
Thanks for putting in the time and helping improve axios-vcr.
A few points:

• I tend to write my OSS using ES5 like syntax in order to broaden the support I can offer in terms of older versions of Node. I think it is actually ok to use a more modern syntax though since Node LTS has changed recently. But I would prefer that we used a different PR for that.

• As for 6a818ac
  Are we still covering the original problem I ran into when I added those comments and that implementation?

• As for 6a818ac
  what's your motivation and use-case here?

I would prefer to see a separate PR for this, so I can understand the use-case, provide feedback and document the new feature.
Also, by merging this feature first, we could issue a non-breaking release of axios-vcr that would allow current users of the library to get this feature without having to do a full upgrade.

• As for adding ESLint and converting the code, I would also prefer to have a separate discussion about that. I tend to prefer using prettier and standard as my formatting and linter, so all my codebases are consistent with the same style.

Please don't take my feedback as criticism of your work. I'm very happy to see more people interested in my library 😄

[nettofarah]

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