README.md in async-1.9.1 vs README.md in async-1.10.0

@@ -108,10 +108,10 @@
 ## Supported Ruby Versions
 
 This library aims to support and is [tested against][travis] the following Ruby
 versions:
 
-* Ruby 2.0+
+* Ruby 2.2+
 * JRuby 9.1.6.0+
 
 If something doesn't work on one of these versions, it's a bug.
 
 This library may inadvertently work (or seem to work) on other Ruby versions,