Update basic-app.Rmd (#471)

To match prerequisites listed in https://github.com/hadley/mastering-shiny/blob/98f1fd1c9521ffe5d518067b40f997a20f8be5f1/introduction.Rmd#L117

Author: luizaandrade

basic-app.Rmd

@@ -18,7 +18,7 @@ If you haven't already installed Shiny, install it now with:
 install.packages("shiny")
 ```
 
-If you've already installed Shiny, use `packageVersion("shiny")` to check that you have version 1.5.0 or greater.
+If you've already installed Shiny, use `packageVersion("shiny")` to check that you have version 1.6.0 or greater.
 
 Then load in your current R session: