Replace eslintConfig with eslint in package.json config

[alexeyraspopov]

Hey guys! At first I want to thank you all, who participate in creating this tool. I'm using it everyday and I appreciate the work you're doing.

I'm not that good in contributing and this change request won't be technical. But I hope it will reduce the level of entropy in the world and make the usage more predictable.

What version of ESLint are you using?
2.5.3

What parser (default, Babel-ESLint, etc.) are you using?
default

And here is my "pain":

Yes, I might be too picky about this thing, but I do believe that at some point of time imaginary user will add eslint key instead of eslintConfig subconsciously, expecting the same result as other tools.

I propose to change this key to eslint or at least support both options (eslint and eslintConfig) untill next major version).

I hope you'll understand me and won't be laughing about probably useless request.

[nzakas]

Duplicate of #2670