fixed link to worksheets in preface

Author: trevorcampbell

preface-text.Rmd

@@ -53,7 +53,7 @@ to help you practice the concepts you will learn. We strongly recommend that you
 work through the worksheet when you finish reading each chapter 
 before moving on to the next chapter. All of the worksheets
 are available at 
-[https://github.com/UBC-DSCI/data-science-a-first-intro-worksheets](https://github.com/UBC-DSCI/data-science-a-first-intro-worksheets);
+[https://ubc-dsci.github.io/data-science-a-first-intro-worksheets](https://ubc-dsci.github.io/data-science-a-first-intro-worksheets);
 the "Exercises" section at the end of each chapter points you to the right worksheet for that chapter.
 The worksheets are designed to provide automated feedback and help guide you through the problems.
 To make sure that functionality works as intended, make sure to follow the setup directions