Test php 7.3

Author: GeorgosXL

.travis.yml

@@ -32,6 +32,7 @@ matrix:
         - php: 7.0
         - php: 7.1
         - php: 7.2
+        - php: 7.3
           env: COVERAGE=true TEST_COMMAND="composer test-ci"
 
           # Test LTS versions