Test against legacy PHP 5.3 through PHP 7.3

Author: clue

.travis.yml

@@ -1,14 +1,22 @@
 language: php
 
 php:
-  - 5.3
+# - 5.3 # requires old distro
   - 5.4
   - 5.5
   - 5.6
-  - 7
-  - hhvm
+  - 7.0
+  - 7.1
+  - 7.2
+  - 7.3
 
-sudo: false
+# lock distro so new future defaults will not break the build
+dist: trusty
+
+matrix:
+  include:
+    - php: 5.3
+      dist: precise
 
 install:
   - composer install --no-interaction

README.md

@@ -390,6 +390,10 @@ The recommended way to install this library is [through composer](http://getcomp
 }
 ```
 
+This project aims to run on any platform and thus does not require any PHP
+extensions and supports running on legacy PHP 5.3 through current PHP 7+.
+It's *highly recommended to use PHP 7+* for this project.
+
 ## Tests
 
 To run the test suite, you first need to clone this repo and then install all