add travis

.travis.yml

@@ -0,0 +1,19 @@
+language: php
+sudo: false
+php:
+  - 5.6
+  - 7
+  - 7.1
+install:
+  - travis_retry composer install --prefer-dist
+script:
+  - vendor/bin/phpunit
+after_script:
+  - travis_retry php vendor/bin/coveralls -v
+after_success:
+  - >-
+    test $TRAVIS_PULL_REQUEST == "false" && test $TRAVIS_BRANCH == "master" &&
+    test $TRAVIS_PHP_VERSION = "7.1" && bash ./scripts/api.sh
+cache:
+  directories:
+    - $HOME/.composer/cache