Use tidyverse package

Fixes #451

strings.Rmd

@@ -6,11 +6,11 @@ This chapter introduces you to string manipulation in R. You'll learn the basics
 
 ### Prerequisites
 
-This chapter will focus on the __stringr__ package for string manipulation. We'll also show a couple of examples of using stringr functions in conjunction with dplyr.
+This chapter will focus on the __stringr__ package for string manipulation. stringr is not part of the core tidyverse because you don't always have textual data, so we need to load it explicitly.
 
-```{r setup}
+```{r setup, message = FALSE}
+library(tidyverse)
 library(stringr)
-library(dplyr)
 ```
 
 ## String basics