Upgrade to PHP 7.2

Author: dcsg

.gitignore

@@ -2,3 +2,4 @@ composer.lock
 vendor/
 phpcs.xml
 phpunit.xml
+/.phpunit.result.cache

.travis.yml

@@ -6,7 +6,6 @@ language: php
 sudo: false
 
 php:
-  - 7.1
   - 7.2
   - 7.3
 

README.md

@@ -1,6 +1,6 @@
 # Minimalist and Typed Immutable Collections for PHP
 
-[![Minimum PHP Version](https://img.shields.io/badge/php-%3E%3D7.1-blue.svg)](https://php.net/)
+[![Minimum PHP Version](https://img.shields.io/badge/php-%3E%3D7.2-blue.svg)](https://php.net/)
 [![Latest Stable Version](https://poser.pugx.org/dcsg/php-immutable-collections/v/stable)](https://packagist.org/packages/dcsg/php-immutable-collections)
 [![License](https://poser.pugx.org/dcsg/php-immutable-collections/license)](https://packagist.org/packages/dcsg/php-immutable-collections)
 [![Build Status](https://travis-ci.org/dcsg/php-immutable-collections.svg?branch=master)](https://travis-ci.org/dcsg/php-immutable-collections)
@@ -17,7 +17,7 @@ A library that provides a set of minimalist, typed and piped Immutable Collectio
 
 ###### Requirements
 
-PHP > 7.1
+PHP > 7.2
 
 ###### Installation
 

composer.json

@@ -17,10 +17,10 @@
     }
   ],
   "require": {
-    "php": "^7.1"
+    "php": "^7.2"
   },
   "require-dev": {
-    "phpunit/phpunit": "^7",
+    "phpunit/phpunit": "^8",
     "squizlabs/php_codesniffer": "^3.0"
   },
   "autoload": {