Updates env in .travis.yaml

Author: flovilmart

.travis.yml

@@ -5,8 +5,8 @@ language: node_js
 node_js:
   - "4.3"
 env:
-  - MONGODB_VERSION=2.6.11
-  - MONGODB_VERSION=3.0.8
+  - MONGODB_VERSION=2.6.11 CODE_COVERAGE=1
+  - MONGODB_VERSION=3.0.8 CODE_COVERAGE=1
 cache:
   directories:
     - $HOME/.mongodb/versions/downloads