function HighlandTransform(push) {
    this.push = push;
}
Same as [scan](#scan), but uses the first element as the initial
state instead of passing in a `memo` value.

@id scan1
@section Transforms
@name Stream.scan1(iterator)
@param {Function} iterator - the function which reduces the values
@api public

_([1, 2, 3, 4]).scan1(add)  // => 1, 3, 6, 10