added loading of dplyr library to Regression Models lesson 1 rmd file in...

...dex to properly recognize variable names in function calls

this was causing some issues running from the index file.

After plaguing me for 30 minutes I hit the discussions to find others with the problem and thought it would be cool to actually contribute to something this awesome.

Knew I recognized the way variable names were being called from a past class (probably exploratory data analysis or cleaning data).