change README to Java 8 requirement

Author: fluentfuture

README.md

@@ -1,7 +1,7 @@
 Disclaimer: This is not an official Google product.
 
 # MµG
-A small Java 9 utilities library ([javadoc](http://google.github.io/mug/apidocs/index.html)), with 0 deps. ![](https://travis-ci.org/google/mug.svg?branch=master)
+A small Java 8 utilities library ([javadoc](http://google.github.io/mug/apidocs/index.html)), with 0 deps. ![](https://travis-ci.org/google/mug.svg?branch=master)
 
 * Stream utilities ([BiStream](#bistream-streams-pairs-of-objects), [MoreStreams](#morestreams)).
 * [Optionals](#optionals) provides extra utilities for java.util.Optional.