Update travis.yml

- Remove test against PHP 7.1
- Remove PHP 8 lowest setup

Author: joaorobertopb

.travis.yml

@@ -9,9 +9,6 @@ env:
 matrix:
   fast_finish: true
   include:
-    - php: 7.1
-    - php: 7.1
-      env: setup=lowest
     - php: 7.2
     - php: 7.2
       env: setup=lowest