Update .travis.yml

Author: barryvdh

.travis.yml

@@ -36,6 +36,9 @@ matrix:
       env: setup=lowest symfony="^5"
     - php: 7.4
       env: setup=lowest symfony="^5"
+  allow_failures:	   
+    - php: 5.6
+    - php: 7.4
 
 install:
   - if [[ $symfony != '*' ]]; then travis_retry composer require symfony/http-foundation:${symfony} --no-update --no-interaction; fi