Documentation: pack-protocol correct NAK response

In the transport protocol we use NAK to signal the non existence of a
common base, so fix the documentation. This helps readers of the document,
as they don't have to wonder about the difference between NAK and NACK.
As NACK is used in git archive and upload-archive, this is easy to get
wrong.

Signed-off-by: Stefan Beller <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: stefanbeller

Documentation/technical/pack-protocol.txt

@@ -302,7 +302,7 @@ In multi_ack mode:
     ready to make a packfile, it will blindly ACK all 'have' obj-ids
     back to the client.
 
-  * the server will then send a 'NACK' and then wait for another response
+  * the server will then send a 'NAK' and then wait for another response
     from the client - either a 'done' or another list of 'have' lines.
 
 In multi_ack_detailed mode: