fix content-type in REST calls

classes/session.php

@@ -202,7 +202,7 @@ class mod_labnbook_session
             CURLOPT_RETURNTRANSFER => true,
             CURLOPT_CUSTOMREQUEST => $verb,
             CURLOPT_URL => $this->url . "/api/index.php" . $urlPath,
-            CURLOPT_HTTPHEADER, ['Content-Type:application/json', 'Accept:application/json'],
+            CURLOPT_HTTPHEADER => ['Content-Type: application/json', 'Accept: application/json'],
             CURLOPT_POSTFIELDS => json_encode($payload),
         ]);
         $response = curl_exec($curl);