Remove deprecated str_contains function

src/Vatsim/Xml/XmlServiceProvider.php

@@ -1,6 +1,7 @@
 <?php namespace Vatsim\Xml;
 
 use Illuminate\Support\ServiceProvider;
+use Illuminate\Support\Str;
 
 class XmlServiceProvider extends ServiceProvider {
 
@@ -37,7 +38,7 @@ public function register()
 		// Lumen users need to copy the config themselves
 		// And it needs to pulled completely differently.
 		// So more work required. Luckily barryvdh had the answer - so thanks.
-		if(str_contains($this->app->version(), "Lumen")){
+		if(Str::contains($this->app->version(), "Lumen")){
 			$this->app->configure("vatsim-xml");
 		} else {
 			$this->publishes([