Update Travis config to remove PHP 7.1 from Symfony 5 builds

Author: emodric

.travis.yml

@@ -1,7 +1,6 @@
 language: php
 
 php:
-    - 7.1
     - 7.2
     - 7.3
 
@@ -10,6 +9,13 @@ env:
     - SYMFONY_VERSION=4.4.*
     - SYMFONY_VERSION=5.0.*
 
+matrix:
+    include:
+        - php: 7.1
+          env: SYMFONY_VERSION=3.4.*
+        - php: 7.1 
+          env: SYMFONY_VERSION=4.4.*
+
 cache:
     directories:
         - ~/.composer/cache/files