Updating PHPUnit to v8.0. Making min PHP version 7.4

.gitignore

@@ -1,3 +1,2 @@
 vendor/
-
-composer.lock
+.phpunit.result.cache

README.md

@@ -8,24 +8,20 @@ __DO NOT USE FOR PASSWORD AUTHENTICATION!__
 
 ### Composer
 
-```
-
+```bash
 composer require affinity4/cipher
-
 ```
 
 ## Usage
 
-```
-
+```php
 // Used by both excrypt and decrypt methods, so should be available globally
 // Perhaps as an environment variable
 $key = 'b1f1e6225cb2b6d0230b16125e45ca63';
 $str = 'my secret';
 
 $encrypted = \Affinity4\Cipher\Cipher::encrypt($str, $key); // piqwpeiqep12801aqwie0248quqjowq==
 $decrypted = \Affinity4\Cipher\Cipher::decrypt($encrypted, $key); // my secret
-
 ```
 
 ## Licence

composer.json

@@ -9,10 +9,10 @@
         }
     ],
     "require": {
-        "php": ">=5.6"
+        "php": ">=7.4"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.5"
+        "phpunit/phpunit": "^8.0"
     },
     "autoload": {
         "psr-4": {