Merge pull request #74 from mariusvw/master

Test against newer php versions.
Resolves #72 and #73

.travis.yml

@@ -13,6 +13,8 @@ matrix:
         - php: 5.6
         - php: 7
         - php: 7.1
+        - php: 7.2
+        - php: 7.3
     fast_finish: true
 
 before_install:
@@ -25,4 +27,4 @@ script:
     - vendor/bin/phpunit --bootstrap vendor/autoload.php --coverage-clover build/logs/clover.xml tests/
 
 after_success:
-  - travis_retry php vendor/bin/coveralls
+  - travis_retry php vendor/bin/coveralls