Follow travis doc for running php 5.3

Author: redthor

.travis.yml

@@ -12,6 +12,8 @@ env:
 
 matrix:
   include:
+    - php: 5.3
+      dist: precise
     - php: 7.0
       env: ADAPTER_VERSION="^1.0.0" MONGODB_VERSION=stable
 
@@ -25,4 +27,4 @@ before_script:
   - composer install --dev
 
 script:
-  - ./vendor/bin/phpunit
+  - ./vendor/bin/phpunit