chore: update main.go

main.go

@@ -72,7 +72,10 @@ func request(client *http.Client, method, url string, body interface{}) (*http.R
     }
 
     req.Header.Set("X-API-KEY", portainerToken)
+    if method != "GET" {
         req.Header.Set("Content-Type", "application/json")
+    }
+
     return client.Do(req)
 }