Update README.md

Fix link to Challenge Jupyter Notebook

Author: flegaspi700

2-Working-With-Data/08-data-preparation/README.md

@@ -315,7 +315,7 @@ letters	numbers
 
 ## 🚀 Challenge
 
-All of the discussed materials are provided as a [Jupyter Notebook](https://https://github.com/microsoft/Data-Science-For-Beginners/blob/main/2-Working-With-Data/08-data-preparation/notebook.ipynb). Additionally, there are exercises present after each section, give them a try!
+All of the discussed materials are provided as a [Jupyter Notebook](https://github.com/microsoft/Data-Science-For-Beginners/blob/main/2-Working-With-Data/08-data-preparation/notebook.ipynb). Additionally, there are exercises present after each section, give them a try!
 
 ## [Post-Lecture Quiz](https://red-water-0103e7a0f.azurestaticapps.net/quiz/15)