fix(tooltip) fix options.target not being passed as DOMElement to dimensions.position

The error occurs as options.target is validated via `angular.isElement` [tooltip.js#L131](https://github.com/SimeonC/angular-strap/blob/e738c9dc4f3e562801aaf82c878b78a6da0ac0c8/src/tooltip/tooltip.js#L131) which requires a valid jQlite/jquery wrapped DOMElement, this gives an error in getPosition() as dimensions.position requires an unwrapped DOMElement.