Fix formatting in 5D.md for REGISTER line

Author: dskvr

5D.md

@@ -67,7 +67,7 @@ Authentication is MUST. All shells and napplets MUST implement the handshake def
 ```
 Napplet                              Shell
   |                                    |
-  |--- REGISTER {nappletType, hash} -------->|
+  |--- REGISTER {nappletType, hash} -->|
   |                                    |  derive keypair
   |<--- IDENTITY {pub, priv} ----------|
   |<--- AUTH <challenge> --------------|