doc: remove repeated a word

PR-URL: #42138
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Mestery <mestery@protonmail.com>

Author: apeltop

doc/api/dgram.md

@@ -844,7 +844,7 @@ travel through. Each router or gateway that forwards a packet decrements the
 TTL. If the TTL is decremented to 0 by a router, it will not be forwarded.
 Changing TTL values is typically done for network probes or when multicasting.
 
-The `ttl` argument may be between between 1 and 255. The default on most systems
+The `ttl` argument may be between 1 and 255. The default on most systems
 is 64.
 
 This method throws `EBADF` if called on an unbound socket.