Update README.md

Author: byjg

.travis.yml

@@ -11,4 +11,4 @@ install:
   - composer install
 
 script: 
-  - phpunit
+  - phpunit --stderr

README.md

@@ -69,8 +69,10 @@ Just type: `composer require "byjg/cache-engine=3.0.*"`
 ## Running Unit Testes
 
 ```
-phpunit
+phpunit --stderr
 ```
 
+**Note:** the parameter `--stderr` after `phpunit` is to permit run the tests on SessionCacheEngine.  
+
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 [Open source ByJG](http://opensource.byjg.com)