Add Travis configuration file to the repository

For now, using it only to run PHPCS.

plugins/woocommerce-beta-tester/.travis.yml

@@ -0,0 +1,13 @@
+language: php
+
+before_script:
+  - |
+    # Remove Xdebug for a huge performance increase:
+    if [ -f ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/xdebug.ini ]; then
+      phpenv config-rm xdebug.ini
+    else
+      echo "xdebug.ini does not exist"
+    fi
+
+script:
+  - ./vendor/bin/phpcs -s -n -p *