.travis.yml: test php 5.3, 5.4, 5.5

Author: ek9

.travis.yml

@@ -1,6 +1,9 @@
 language: php
 matrix:
   include:
+    - php: 5.3
+    - php: 5.4
+    - php: 5.5
     - php: 5.6
     - php: 5.6
       env: deps=low