Updated Javascript code snippet to upload an attachment

Updated Javascript code snippet to upload an attachment

docs/sending/attachments.mdx

@@ -43,16 +43,16 @@ Unvollständige Einreichungen, die durch das sendende System (Onlinedienst) nich
 <TabItem value="js">
 
   ```js
-var axios = require('axios');
+const axios = require('axios');
 
-var data = 'eyJhbGciOiJSU0Et...MRPcWqnLJDtp6ZA0Q';
+const data = 'eyJhbGciOiJSU0Et...MRPcWqnLJDtp6ZA0Q';
 
 const SUBMISSION_ID = "a562cf6a-3860-4a7e-96e3-1d01f8a5252d"
 const ATTACHMENT_ID = "12399641-2067-4e8b-b049-91b2a6c90544"
 const TOKEN = "eyJraWQiOiJHb2JOIiwi...Xh1TWcb2uhLVVnDBQ"
 const SUBMISSION_API = "https://submission-api-testing.fit-connect.fitko.dev"
 
-var config = {
+const config = {
   method: 'put',
   url: SUBMISSION_API + '/v1/submissions/' + SUBMISSION_ID + '/attachments/' + ATTACHMENT_ID,
   headers: { 
@@ -63,12 +63,8 @@ var config = {
 };
 
 axios(config)
-.then(function (response) {
-  console.log(JSON.stringify(response.data));
-})
-.catch(function (error) {
-  console.log(error);
-});
+.then(response => console.log(JSON.stringify(response.data)))
+.catch(error => console.log(error));
   ```