Used Symfony Flex in favor of symfony/lts

Author: wouterj

.travis.yml

@@ -17,14 +17,14 @@ matrix:
     - php: 7.1
       env: COMPOSER_FLAGS="--prefer-lowest" SYMFONY_DEPRECATIONS_HELPER=weak
     - php: 7.1
-      env: SYMFONY_LTS=^3
+      env: SYMFONY_REQUIRE="3.*"
     - php: 7.2
     - php: 7.3
       env: DEPENDENCIES=dev
 
 before_install:
     - phpenv config-rm xdebug.ini
-    - if [ "$SYMFONY_LTS" != "" ]; then composer require --dev --no-update "symfony/lts:$SYMFONY_LTS"; fi
+    - composer global require --no-progress --no-scripts --no-plugins symfony/flex dev-master
     - if [ "$DEPENDENCIES" = "dev" ]; then composer config minimum-stability dev; fi;
 
 install: