Specifying PHP versions

.travis.yml

@@ -5,9 +5,10 @@ os:
   - windows
 
 php:
-  - 5.3
-  - 5.4
-  - 5.5
+  - 5.3.29
+  - 5.4.45
+  - 5.5.29
+  - 5.6.13
 
 before_script:
   - composer self-update