correct onPageChange index

[antonzy]

incorrect page index was passed to the onPageChange handler

[LzxHahaha]

I think Swiper.android.js should be like this

if (page != lastPage){
  page = this.props.loop ? page - 1 : page;
  this.setState({
    index: page,
  });
  this.props.onPageChanged && this.props.onPageChanged(page);
}

[sunnylqm]

@tdzl2003