Fix incorrect namespace prefix set for stream:error.

This was setting xmlns:streams, leaving stream:error with an undefined
namespace prefix.

plugins/mod_bosh.lua

@@ -383,7 +383,7 @@ local function bosh_close_stream(session, reason)
 	(session.log or log)("info", "BOSH client disconnected");
 
 	local close_reply = st.stanza("body", { xmlns = xmlns_bosh, type = "terminate",
-		["xmlns:streams"] = xmlns_streams });
+		["xmlns:stream"] = xmlns_streams });
 
 
 	if reason then