useless line in the _Quiver class definition

In the _Quiver class definition (more precisely within the body of one of its methods) there is a useless line https://github.com/plotly/plotly.py/blob/master/packages/python/plotly/plotly/figure_factory/_quiver.py#L257 which just leads to repeating the calculations of the elements in the four lists under the for loop:

for index in range(len(self.end_x)):
    point1_x = [i - j * self.scaleratio for i, j in zip(self.end_x, seg1_x)]
    point1_y = [i - j for i, j in zip(self.end_y, seg1_y)]
    point2_x = [i - j * self.scaleratio for i, j in zip(self.end_x, seg2_x)]
    point2_y = [i - j for i, j in zip(self.end_y, seg2_y)]

The for line must be removed and the next four lines moved a tab at left.

打开 packages/python/plotly/plotly/figure_factory/_quiver.py 的第257行，并检查周围的 _Quiver 方法。删除循环行，并按要求将列出的四个赋值移到外部。完成的标志是计算只执行一次，而不是针对每个索引重复执行；之后验证现有的 quiver 行为。