Remove disclaimer about out-of-date book (documentationjs#359)

Now compatible with 13.x

Author: milesfrain

README.md

@@ -16,7 +16,7 @@ This repository is a collaborative effort, so please feel free to make a pull re
 
 ### Learning
 
-- The [PureScript Book](https://book.purescript.org) is the recommended approach to learning the language, since it covers more material in greater depth. However, it is currently being updated from the `0.11.7` version of the PureScript compiler to the `0.13.x` version.
+- The [PureScript Book](https://book.purescript.org) is the recommended approach to learning the language, since it covers more material in greater depth.
 - [Language Reference](language/README.md)
 - [PureScript: Jordan's Reference](https://github.com/JordanMartinez/purescript-jordans-reference): An up-to-date project covering Getting Started, Build Tools, PureScript's syntax with examples, FP design patterns, and PureScript's ecosystem.
 - [PureScript Cookbook](https://github.com/JordanMartinez/purescript-cookbook): An unofficial cookbook for PureScript.