Fix downloads badge (#3266)

*Issue #, if available:* Badge showing monthly downloads broke.

*Description of changes:* Update README using latest URL for the badge
from pepy.tech.


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dev setup

Author: lostella

README.md

@@ -6,7 +6,7 @@
 [![GitHub](https://img.shields.io/github/license/awslabs/gluonts.svg?style=flat-square&color=df7e66)](./LICENSE)
 [![Static](https://img.shields.io/static/v1?label=docs&message=stable&color=edc775&style=flat-square)](https://ts.gluon.ai/)
 [![Static](https://img.shields.io/static/v1?label=docs&message=dev&color=edc775&style=flat-square)](https://ts.gluon.ai/dev/)
-[![PyPI Downloads](https://img.shields.io/pypi/dm/gluonts?style=flat-square&color=94b594)](https://pepy.tech/project/gluonts)
+[![PyPI Downloads](https://static.pepy.tech/badge/gluonts/month)](https://pepy.tech/projects/gluonts)
 
 **📢 BREAKING NEWS**: We released **Chronos**, a suite of pretrained models for zero-shot time series forecasting. Chronos can generate accurate probabilistic predictions for new time series not seen during training. Check it out [here](https://github.com/amazon-science/chronos-forecasting)!