Remove travis tests for symfony 2.5/6 due to EOL reached

Author: Luis Pabon

.travis.yml

@@ -15,10 +15,6 @@ matrix:
       env: COMPOSER_FLAGS="--prefer-lowest"
     - php: 5.6
       env: SYMFONY_VERSION=2.3.*
-    - php: 5.6
-      env: SYMFONY_VERSION=2.5.*
-    - php: 5.6
-      env: SYMFONY_VERSION=2.6.*
     - php: 5.6
       env: SYMFONY_VERSION=2.7.*
     - php: 5.6