Merge pull request #224 from alcaeus/test-all-driver-versions

Test against 1.3 version of mongodb driver

.travis.yml

@@ -13,6 +13,9 @@ php:
 env:
   global:
     - DRIVER_VERSION="stable"
+  matrix:
+    - DRIVER_VERSION="stable"
+    - DRIVER_VERSION="1.3.4"
 
 addons:
   apt: