Inconsistent Array Declaration

This PR normalises the declaration of arrays throughout the project, and adds
this to the php-cs-fixer rules.

I've chosen "short" by default, but happy to change the PR to use "long" if
preferred.

src/Configurations/PageRulesActions.php

@@ -10,7 +10,7 @@ namespace Cloudflare\API\Configurations;
 
 class PageRulesActions implements Configurations
 {
-    private $configs = array();
+    private $configs = [];
 
     public function setAlwaysOnline(bool $active)
     {

src/Configurations/UARules.php

@@ -10,7 +10,7 @@ namespace Cloudflare\API\Configurations;
 
 class UARules implements Configurations
 {
-    private $configs = array();
+    private $configs = [];
 
     public function addUA(string $value)
     {

src/Configurations/ZoneLockdown.php

@@ -10,7 +10,7 @@ namespace Cloudflare\API\Configurations;
 
 class ZoneLockdown implements Configurations
 {
-    private $configs = array();
+    private $configs = [];
 
     public function addIP(string $value)
     {