chore: add PHP 7.4 to Travis and test with lowest dependencies (#140)

Author: childish-sambino

.travis.yml

@@ -1,5 +1,9 @@
 language: php
 
+before_script:
+  - composer install
+  - if [ "$dependencies" = "lowest" ]; then composer update --prefer-lowest --prefer-stable -n; fi;
+
 script:
   - make test
 
@@ -12,3 +16,8 @@ php:
   - 7.1
   - 7.2
   - 7.3
+  - 7.4
+
+env:
+  - dependencies=lowest
+  - dependencies=highest

README.md

@@ -30,7 +30,7 @@ All updates to this library are documented in our [CHANGELOG](https://github.com
 
 ## Prerequisites
 
-- PHP version 5.6 or higher
+- PHP version 5.6, 7.0, 7.1, 7.2, 7.3, or 7.4
 
 ## Install with Composer