Travis integration #120 (#159)

* fixed php versions used in travis #120
* fixed broken test #120
* updated developer docu

.travis.yml

@@ -8,12 +8,8 @@ cache:
 matrix:
   fast_finish: true
   include:
-    - php: 5.5
-    - php: 5.6
-    - php: 7.0
-    - php: hhvm
-  allow_failures:
-    - php: hhvm
+    - php: 7.1
+    - php: 7.2
 
 before_install:
   - if [[ "$TRAVIS_PHP_VERSION" != "hhvm" ]]; then phpenv config-rm xdebug.ini; fi
@@ -23,4 +19,5 @@ install:
   - composer install
 
 script:
-  - phpunit
+  - vendor/bin/phpunit --exclude-group integration tests/
+  - vendor/bin/phpunit --group integration tests/