Add travis build image.

Spencer Rinehart · Spencer Rinehart · commit 58558aa72858 · 2014-03-13T11:25:41.000-04:00
diff --git a/README.md b/README.md
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 # Memoize
 A PHP library for memoizing repeated function calls.
 
+[![Build Status](https://travis-ci.org/dominionenterprises/memoize-php.png)](https://travis-ci.org/dominionenterprises/memoize-php)
+
 ## Requirements
 This library requires PHP 5.3, or newer.
 
