message: fixes ExtVersion docs
diff: @@ -214,7 +214,7 @@ a non zero suffix as a key.
  ### Bitcoin Unlimited
  In the Bitcoin Unlimited reference implementation, the `xversion`
  -message is handled using the `CXVersionMessage` class. The actual
  +message is handled using the `CExtversionMessage` class. The actual
  `xmap` is serialized and deserialized using the
  `CompactMapSerialization` adapter class. To avoid attacks that could
  cause a slow-down of key lookup in the `xmap` tables, the table is
  