Fix from lightning#306

Added fix for duplicate word courtesy of @dimitris-t in lightning#306.

Author: Shannon Appelcline

08-transport.md

@@ -411,7 +411,7 @@ The *maximum* size of _any_ Lightning message MUST NOT exceed `65535` bytes. A
 maximum size of `65535` simplifies testing, makes memory management 
 easier, and helps mitigate memory-exhaustion attacks.
 
-In order to make make traffic analysis more difficult, the length prefix for
+In order to make traffic analysis more difficult, the length prefix for
 all encrypted Lightning messages is also encrypted. Additionally a
 16-byte `Poly-1305` tag is added to the encrypted length prefix in order to ensure
 that the packet length hasn't been modified when in-flight and also to avoid