function stripNested (prop, str, val) {
  return str.replace(new RegExp('(\\.)?' + prop, 'g'), function($0, $1) {
    return $1 ? $0 : val;
  });
}
Mimic negative lookbehind to avoid problems with nested properties.

See: http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript

@param {String} prop
@param {String} str
@param {String} val
@return {String}
@api private