Try making dev version resolving a little bit easier

Author: wouterj

.travis.yml

@@ -20,7 +20,7 @@ matrix:
     - php: 5.6
       env: SYMFONY_VERSION=2.8.* COMPOSER_FLAGS="--prefer-lowest" SYMFONY_DEPRECATIONS_HELPER=weak
     - php: 7.1
-      env: DEPS=dev
+      env: SYMFONY_VERSION=3.3.* DEPS=dev
     - php: 7.1
       env: SYMFONY_VERSION=3.1.*
   fast_finish: true