Test against PHP 7.4 (#18)

* Test against PHP 7.4

* Update .travis.yml

* Test against nightly

* Add ignore platform reqs

* Fix flags

* fix

* ix

* Update README.md

* Update .travis.yml

Author: Ekman

.travis.yml

@@ -5,8 +5,17 @@ php:
   - 7.1
   - 7.2
   - 7.3
+  - 7.4snapshot
+  - nightly
+  - hhvm
+  
+matrix:
+  allow_failures:
+  - php: 7.4snapshot
+  - php: nightly
+  - php: hhvm
 
-install: composer install --no-interaction --classmap-authoritative --no-suggest
+install: composer install --no-interaction --classmap-authoritative --no-suggest --ignore-platform-reqs
 
 script: vendor/bin/phpunit --configuration phpunit.xml
 

README.md

@@ -3,7 +3,7 @@
 [![Build Status](https://travis-ci.org/Ekman/Luhn-Algorithm.svg?branch=master)](https://travis-ci.org/Ekman/Luhn-Algorithm)
 [![Coverage Status](https://coveralls.io/repos/github/Ekman/Luhn-Algorithm/badge.svg)](https://coveralls.io/github/Ekman/Luhn-Algorithm)
 
-This is an implementation of the Luhn Algorithm for PHP. The Luhn Algorithm is
+This is an implementation of the Luhn Algorithm for PHP 7.0 and above. The Luhn Algorithm is
 used to validate things like credit cards and national identification numbers.
 More information on the algorithm can be found at [Wikipedia](http://en.wikipedia.org/wiki/Luhn_algorithm).