add travis configuration

.travis.yml

@@ -0,0 +1,28 @@
+language: php
+php:
+  - 5.6
+  - 5.5
+  - 5.4
+  - 5.3
+  - hhvm
+
+matrix:
+  allow_failures:
+    - php: 5.6
+    - php: hhvm
+
+branches:
+    only:
+        - /^v\d\.\d/
+cache:
+  directories:
+    - vendor
+
+before_script:
+  - composer install --dev --no-interaction
+
+script:
+  - composer run test
+
+after_script:
+  - php vendor/bin/coveralls