Fix env variable name

Author: wouterj

.travis.yml

@@ -15,12 +15,12 @@ cache:
     - $HOME/.composer/cache
 
 env:
-  - SYMFONY_VERSION=2.7.* SYMFONY_DEPRECATION_HELPER=weak
+  - SYMFONY_VERSION=2.7.* SYMFONY_DEPRECATIONS_HELPER=weak
 
 matrix:
   include:
     - php: 5.6
-      env: SYMFONY_VERSION=2.3.* SYMFONY_DEPRECATION_HELPER=weak
+      env: SYMFONY_VERSION=2.3.* SYMFONY_DEPRECATIONS_HELPER=weak
     - php: 5.6
       env: SYMFONY_VERSION=2.8.*
     - php: 5.6