Adding travis config file

.travis.yml

+language: php
+
+php:
+  - 7
+  - 5.6
+
+cache:
+  directories:
+    - $HOME/.composer/cache
+
+env:
+  - LARAVEL_VERSION="~5.3" TESTBENCH_VERSION="~3.3"
+
+before_script:
+  - travis_retry composer self-update
+  - travis_retry composer update ${COMPOSER_FLAGS} --no-interaction --prefer-dist
+
+script: phpunit
+
+sudo: false
+