Updates travis build

Author: pdscopes

.travis.yml

@@ -1,10 +1,11 @@
-os: ubuntu
+os: linux
 dist: xenial
 language: php
 sudo: false
 php:
-  - 7.0
-  - 7.1
+  - 7.2
+  - 7.3
+  - 7.4
 before_script:
   - COMPOSER_DISCARD_CHANGES=1 composer update --prefer-dist --no-interaction --no-suggest
   - cp phpunit.xml.example phpunit.xml