name-server-protocol: fix documentation about nameserver

Change-Id: I4bc0f124daa8cf986ebcaba45ad08e5198ef2adc

developer/name-server-protocol.md

@@ -23,7 +23,7 @@ Usernames are checked by a regex to ensure some rules about their
 format:
 
 -   Length must be between 3 and 32 characters
--   Those characters must be alphanumerical with underscore `_` being
+-   Those characters must be alphanumerical with dashes `-` being
     also accepted.
 
 Querying a name