Update .travis.yml

Author: pulkitjalan

.travis.yml

@@ -4,6 +4,7 @@ php:
   - 7.0
   - 7.1
   - 7.2
+  - 7.3
 
 sudo: false
 
@@ -16,4 +17,4 @@ script:
 
 after_script:
   - wget https://scrutinizer-ci.com/ocular.phar
-  - php ocular.phar code-coverage:upload --format=php-clover coverage.clover
+  - php ocular.phar code-coverage:upload --format=php-clover coverage.clover