fix signature (#712)

Note sure where the other one was coming from.

-> https://gchq.github.io/CyberChef/#recipe=HMAC(%7B'option':'UTF8','string':'secret'%7D,'SHA256')From_Hex('None')To_Base64('A-Za-z0-9-_')&input=aGVsbG8vcnM6ZmlsbDozMDA6NDAwOjAvZzpzbS9hSFIwY0RvdkwyVjRZVzF3L2JHVXVZMjl0TDJsdFlXZGwvY3k5amRYSnBiM05wZEhrdS9hbkJuLnBuZw

docs/signing_the_url.md

@@ -57,13 +57,13 @@ hello/rs:fill:300:400:0/g:sm/aHR0cDovL2V4YW1w/bGUuY29tL2ltYWdl/cy9jdXJpb3NpdHku/
 Then calculate the HMAC digest of this string using SHA256 and encode it with URL-safe Base64:
 
 ```
-LzIKNN09Lv_LAJhmgqbC6_VFlm0qlW2El5riObZq3BQ
+oKfUtW34Dvo2BGQehJFR4Nr0_rIjOtdtzJ3QFsUcXH8
 ```
 
 And finally put the signature to your URL:
 
 ```
-http://imgproxy.example.com/LzIKNN09Lv_LAJhmgqbC6_VFlm0qlW2El5riObZq3BQ/rs:fill:300:400:0/g:sm/aHR0cDovL2V4YW1w/bGUuY29tL2ltYWdl/cy9jdXJpb3NpdHku/anBn.png
+http://imgproxy.example.com/oKfUtW34Dvo2BGQehJFR4Nr0_rIjOtdtzJ3QFsUcXH8/rs:fill:300:400:0/g:sm/aHR0cDovL2V4YW1w/bGUuY29tL2ltYWdl/cy9jdXJpb3NpdHku/anBn.png
 ```
 
 Now you got the URL that you can use to resize the image securely.