function toPlainObject(value) {
  return copyObject(value, keysIn(value));
}
Converts `value` to a plain object flattening inherited enumerable string
keyed properties of `value` to own properties of the plain object.

@static
@memberOf _
@since 3.0.0
@category Lang
@param {*} value The value to convert.
@returns {Object} Returns the converted plain object.
@example

function Foo() {
  this.b = 2;
}

Foo.prototype.c = 3;

_.assign({ 'a': 1 }, new Foo);
// => { 'a': 1, 'b': 2 }

_.assign({ 'a': 1 }, _.toPlainObject(new Foo));
// => { 'a': 1, 'b': 2, 'c': 3 }