Adding a basic Travis file

Author: eaarranz

.travis.yml

@@ -0,0 +1,15 @@
+language: php
+php:
+  - 7.1
+  - 7.2
+  - 7.3
+
+sudo: false
+
+cache:
+  directories:
+    - vendor
+    - $HOME/.composer/cache
+
+install:
+  - composer install