fix startY bug
fix startY bug

TotooriaHyperion/better-scroll,neurotoxinvx/better-scroll,ustbhuangyi/better-scroll,TotooriaHyperion/better-scroll,ustbhuangyi/better-scroll,TotooriaHyperion/better-scroll,neurotoxinvx/better-scroll,ustbhuangyi/better-scroll,neurotoxinvx/better-scroll,ustbhuangyi/better-scroll