Numpy dependency version needs to be bumped to 1.20.x for numpy.typing

[winedarksea]

Or else the typing import needs to be removed (it isn't strictly necessary for any functionality).

I can open a PR for this, it's pretty simple, but I think someone needs to answer the question of whether a dependency version bump or the need for typing is more important.

prophet/python/prophet/forecaster.py

Line 18 in c00f6a2

from numpy.typing import NDArray

on np<1.20, an error occurs, module not found.