initWithScrollView:delegate: should call initWithFrame: on super, not self

[vadim-fueled]

Since initWithScrollView:delegate: is a de-facto designated initializer it should call designated initializer of superclass with super, not self
Explicitly stating that it's a designated initializer with NS_DESIGNATED_INITIALIZER would be nice.

[vadim-fueled]

Did this not result in a warning at https://github.com/soffes/sspulltorefresh/blob/3ee6473e1f35c8c1eab8c28c933592141a8a9759/SSPullToRefresh/SSPullToRefreshView.m#L161
which is my original complaint?
The thing is I can't subclass SSPullToRefreshView in Swift without overriding init(frame:) which is odd.

[soffes]

Fixed that in 68ac0ee