[DOC] fix broken download badges in README (#334)

Replaces the broken pepy.tech download badges by shield.io badges to
measure pypi downloads.

README.md

@@ -14,7 +14,7 @@ along with tools to make it easier to build your own packages that follow these
 |---|---|
 | **CI/CD** | [![Tests](https://github.com/sktime/skbase/actions/workflows/test.yml/badge.svg?branch=main)](https://github.com/sktime/skbase/actions/workflows/test.yml) [![codecov](https://codecov.io/gh/sktime/skbase/branch/main/graph/badge.svg?token=2J424NLO82)](https://codecov.io/gh/sktime/skbase) [![Documentation Status](https://readthedocs.org/projects/skbase/badge/?version=latest)](https://skbase.readthedocs.io/en/latest/?badge=latest) [![pre-commit.ci status](https://results.pre-commit.ci/badge/github/sktime/skbase/main.svg)](https://results.pre-commit.ci/latest/github/sktime/skbase/main) |
 | **Code** |  [![!pypi](https://img.shields.io/pypi/v/scikit-base?color=orange)](https://pypi.org/project/scikit-base/)  [![!python-versions](https://img.shields.io/pypi/pyversions/scikit-base)](https://www.python.org/) [![!black](https://img.shields.io/badge/code%20style-black-000000.svg)](https://github.com/psf/black) [![security: bandit](https://img.shields.io/badge/security-bandit-yellow.svg)](https://github.com/PyCQA/bandit) |
-| **Downloads** | [![Downloads](https://static.pepy.tech/personalized-badge/scikit-base?period=week&units=international_system&left_color=grey&right_color=blue&left_text=weekly%20(pypi))](https://pepy.tech/project/scikit-base) [![Downloads](https://static.pepy.tech/personalized-badge/scikit-base?period=month&units=international_system&left_color=grey&right_color=blue&left_text=monthly%20(pypi))](https://pepy.tech/project/scikit-base) [![Downloads](https://static.pepy.tech/personalized-badge/scikit-base?period=total&units=international_system&left_color=grey&right_color=blue&left_text=cumulative%20(pypi))](https://pepy.tech/project/scikit-base) |
+| **Downloads** | ![PyPI - Downloads](https://img.shields.io/pypi/dw/scikit-base) ![PyPI - Downloads](https://img.shields.io/pypi/dm/scikit-base) [![Downloads](https://static.pepy.tech/personalized-badge/scikit-base?period=total&units=international_system&left_color=grey&right_color=blue&left_text=cumulative%20(pypi))](https://pepy.tech/project/scikit-base) |
 | **Citation** | [![DOI](https://zenodo.org/badge/494649836.svg)](https://zenodo.org/doi/10.5281/zenodo.10980557) |
 
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