Added php7 to travis.yml

Author: mschindler

.travis.yml

@@ -10,6 +10,8 @@ env:
 
 matrix:
   include:
+    - php: 7.0
+      env: PAYMILL_WH_1=subscription.failed PAYMILL_WH_2=subscription.expiring
     - php: 5.6
       env: PAYMILL_WH_1=transaction.succeeded PAYMILL_WH_2=subscription.created
     - php: 5.5