Remove old message about compiler version

Author: garyb

README.md

@@ -4,7 +4,7 @@
 [![Build Status](https://travis-ci.org/purescript/purescript-st.svg?branch=master)](https://travis-ci.org/purescript/purescript-st)
 [![Dependency Status](https://www.versioneye.com/user/projects/55848ce7363861001d000358/badge.svg?style=flat)](https://www.versioneye.com/user/projects/55848ce7363861001d000358)
 
-The ST effect, for safe local mutation. For use with compiler version >= 0.7.
+The ST effect, for safe local mutation.
 
 ## Installation