in date, "built on" is already in the book template (#92)

index.Rmd

@@ -1,6 +1,6 @@
 --- 
 title: "HTTP testing in R"
-date: "`r paste0('built on ', Sys.Date())`"
+date: "`r Sys.Date()`"
 author: "Scott Chamberlain, Maëlle Salmon"
 site: bookdown::bookdown_site
 documentclass: book
@@ -32,4 +32,4 @@ You can also read the [PDF version](/http-testing/main.pdf) or [epub version](/h
 
 ```{block, type = "alert alert-dismissible alert-success"}
 Project funded by [rOpenSci](https://ropensci.org`) (Scott Chamberlain's work) & the [R Consortium](https://www.r-consortium.org/projects/awarded-projects/2020-group-1#HTTP+testing+in+R+Book) (Maëlle Salmon's work).
-```
+```