Updated .travis.yml with new services param 

SeeĀ http://about.travis-ci.org/blog/august-2012-upcoming-ci-environment-updates/ for details
diff --git a/.travis.yml b/.travis.yml
index 2496def..62acf05 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,6 +3,11 @@
 php:
   - 5.3
   - 5.4
+  
+services:
+  - mysql
+  - postgresql
+  - sqlite
 
 env:
   - DB=mysql