utils/setIn: fix issue when the object has a key that is one of the path's parts

[islam3zzat]

There is currently an issue with the setIn method that happens when the original object has a key
that is part of the provided path

setIn({x: true}, 'a.x.c', false);

and at some point in the setIn function, the currentObj is set to the originalObject[partOfPath]
and if the originalObject has a value for that the currentObj will be set to that value

    const currentPath: string = pathArray[i];
    let currentObj: any = obj[currentPath];

and then resVal will be set to this value

    //...
    } else if (currentObj) {
      resVal = resVal[currentPath] = cloneDeep(currentObj);
    } else {
    //...

and after the loop wee add a property to this value, which will raise an error

 resVal[pathArray[i]] = value;

I've added this test which will validate this issue

    it('supports path containing key of the object', () => {
      const obj = { x: 'y' };
      const newObj = setIn(obj, 'a.x.c', 'value');
      expect(obj).toEqual({ x: 'y' });
      expect(newObj).toEqual({ x: 'y', a: { x: { c: 'value' } } });
    });

which will faill

TypeError: Cannot create property 'c' on string 'y'

[islam3zzat]

@jaredpalmer I've created this sandbox to illustrate how this issue can affect us
https://codesandbox.io/s/rr2ly7wznm