Use sf 4.2 stable version

Author: Jeremiah VALERIE

.travis.yml

@@ -45,7 +45,7 @@ jobs:
         - php: 7.2
           env: SYMFONY_VERSION=4.1.*
         - php: 7.2
-          env: SYMFONY_VERSION=4.2.* STABILITY=beta
+          env: SYMFONY_VERSION=4.2.*
         - php: nightly
           env: COMPOSER_UPDATE_FLAGS=--ignore-platform-reqs
         - php: 7.2