Merge pull request #1089 from stan-dev/readme-remove-beta

Remove use of "beta" from Readme

Author: jgabry

README.md

@@ -34,7 +34,7 @@ analysis.
 
 #### Installing the R package
 
-You can install the latest beta release of the **cmdstanr** R package with
+You can install the latest release of the **cmdstanr** R package with
 
 ```r
 # we recommend running this in a fresh R session or restarting your current session