Remove 'includes' API, fix CI build failure

[Alanscut]

Changes:

1. Error message: "Object doesn't support property or method 'includes' to equal."

2. Reason: 'includes' belongs to the API of ES7, ie11 does not support it.

   https://github.com/axios/axios/blob/master/lib/utils.js#L29

3. Related PR Remove dependency on is-buffer #1816

[yasuf]

what's the difference between using void 0 and undefined?

[Alanscut]

undefined is not a reserved word in javascript, so it can be rewritten. void 0 is stricter.

[yasuf]

we rely on type of x === 'undefined' throughout the file, might be better to be consistent, also are there cases where the constructor can be null? could it be sufficient to just check !isUndefined(val.constructor), also we can just use our own helper? isUndefined, what do you think?

[Alanscut]

I agree to use isUndefined, and I suggest to replace all the other undefined judgement with our own helper function isUndefined, if you agree, then I will submit a PR.

if constructor has been overwriten with null (extreme paticular case), then typeof val.constructor.isBuffer === 'function' will report an error.

[chinesedfan]

@Alanscut Can we simply copy the implementation from is-buffer, as well as its tests? Of course, with a reference comment. That looks clear and simple. And don't change the position of function isUndefined if not necessary.

[Alanscut]

@Alanscut Can we simply copy the implementation from is-buffer, as well as its tests? Of course, with a reference comment. That looks clear and simple. And don't change the position of function isUndefined if not necessary.

@chinesedfan because we have to obey the 3 rules of eslint:

• "no-use-before-define": 2, // http://eslint.org/docs/rules/no-use-before-define
• "eqeqeq": 2, // http://eslint.org/docs/rules/eqeqeq
• "no-eq-null": 2, // http://eslint.org/docs/rules/no-eq-null