Confusing about test case eslint-path

[monkingxue]

Hi, I have some problems about test case 1(eslint-path).
I find a mock eslint in mock directory, but I think it's not enough, because the loader also relies on formatter {formatter: require("eslint/lib/formatters/stylish")}. If I change eslint path, I want to use the formatter in eslint path instead of the original. But the test case only mock the eslint, I think we also need to mock formatter.

[ricardogobbosouza]

@monkingxue
Resolve #275