filterBy on boolean is not working

Filtering on a boolean property has no effect at all.
_Example_: `$filter('filterBy')(collection, ['property'], true)`

Looking at the [source](https://github.com/a8m/angular-filter/blob/master/src/_filter/collection/filter-by.js) we can see that only string and number are allowed.
_Line 14_: `search = (isString(search) || isNumber(search)) ? String(search).toLowerCase() : undefined;`