Update travis

Author: Daan Biesterbos

.travis.yml

@@ -9,8 +9,9 @@ cache:
 matrix:
   fast_finish: true
   include:
-    - php: 7.1
     - php: 7.2
+    - php: 7.3
+    - php: 7.4
 
 before_script:
   - composer self-update