added Travis CI script

.travis.yml

@@ -0,0 +1,13 @@
+# The Travis setup:
+# - run testsuite for every PHP version
+language: php
+php:
+  - '7.1'
+  - '7.0'
+  - '5.6'
+  - hhvm
+install:
+  - composer self-update
+  - composer update --profile --verbose
+after_success:
+  - bash <(curl -s https://codecov.io/bash)