Improve version handling.

app/Services/FireflyIIIOrg/Update/UpdateRequest.php

@@ -42,7 +42,7 @@ class UpdateRequest implements UpdateRequestInterface
      */
     public function getVersion(string $channel): array
     {
-        $uri = 'https://version.firefly-iii.org/index.json';
+        $uri = config('firefly.update_endpoint');
         Log::debug(sprintf('Going to call %s', $uri));
         try {
             $client = new Client();

app/Services/FireflyIIIOrg/Update/UpdateRequestInterface.php

@@ -31,7 +31,7 @@ interface UpdateRequestInterface
     /**
      * @param string $channel
      *
-     * @return string
+     * @return array
      * @throws FireflyException
      */
     public function getVersion(string $channel): array;