flipPrev() does not work when disableFlipByClick is true

[WilliamIsted]

When disableByFlipClick is true, flipNext() does not function. This appears to be a similar issue to #18. https://github.com/Nodlik/StPageFlip/blob/ab30ecc1d9f6d98de1a99b8e296469382f41c120/src/Flip/Flip.ts#L255-L260 This is resolved by replacing line 257 with x: this.render.getRect().left + 10,.