### deepMapKeys

Deep maps an object keys.

Creates an object with the same values as the provided object and keys generated by running the provided function for each key.

Use `Object.keys(obj)` to iterate over the object's keys. 
Use `Array.prototype.reduce()` to create a new object with the same values and mapped keys using `fn`.

```js
const deepMapKeys = (obj, f) => (
  Array.isArray(obj)
    ? obj.map(val => deepMapKeys(val, f))
    : (typeof obj === 'object')
    ? Object.keys(obj).reduce((acc, current) => {
      const val = obj[current];
      acc[f(current)] = (val !== null && typeof val === 'object')
        ? deepMapKeys(val, f)
        : acc[f(current)] = val;
      return acc;
    }, {})
    : obj
);
```

```js
const obj = {
  foo:'1',
  nested:{
    child:{
      withArray:[
        {
          grandChild:[ 'hello' ]
        }
      ]
    }
  }
};
const upperKeysObj = deepMapKeys(obj, (key) => key.toUpperCase());
/*
{
  "FOO":"1",
  "NESTED":{
    "CHILD":{
      "WITHARRAY":[
        {
          "GRANDCHILD":[ 'hello' ]
        }
      ]
    }
  }
}
*/
```