Added TravisCI configuration file

Author: frenck

.travis.yml

@@ -0,0 +1,13 @@
+language: php
+
+php:
+  - 7.0
+  - 5.6
+  - 5.5
+  - 5.4
+
+script:
+  - composer self-update || true
+  - composer validate
+  - composer install
+  - ./vendor/bin/phpunit --version