Added Travis CI

- Created Travis CI configuration
- Added build status badge to README.md

Author: josemmo

.travis.yml

@@ -0,0 +1,21 @@
+language: php
+
+jobs:
+  fast_finish: true
+  include:
+    - php: '7.3'
+    - php: '7.4'
+    - php: '8.0'
+    - php: nightly
+  allow_failures:
+    - php: nightly
+
+install:
+  - pecl install ast
+  - phpenv config-rm xdebug.ini
+  - composer validate --strict
+  - composer install --ignore-platform-reqs --no-interaction
+
+script:
+  - vendor/bin/phan
+  - vendor/bin/phpunit --testdox

README.md

@@ -1,4 +1,5 @@
 # Uncomplicated XML
+[![Build Status](https://travis-ci.com/josemmo/uxml.svg?branch=main)](https://travis-ci.com/josemmo/uxml)
 [![Latest Version](https://img.shields.io/packagist/v/josemmo/uxml)](https://packagist.org/packages/josemmo/uxml)
 [![Minimum PHP Version](https://img.shields.io/packagist/php-v/josemmo/uxml)](#installation)
 [![License](https://img.shields.io/github/license/josemmo/uxml)](LICENSE)