derp: fix varz typo

Updates tailscale/corp#391

derp/derp_server.go

@@ -1132,8 +1132,8 @@ func (s *Server) ExpVar() expvar.Var {
 	m.Set("counter_unique_clients_ever", s.expVarFunc(func() interface{} { return len(s.clientsEver) }))
 	m.Set("gauge_memstats_sys0", expvar.Func(func() interface{} { return int64(s.memSys0) }))
 	m.Set("gauge_watchers", s.expVarFunc(func() interface{} { return len(s.watchers) }))
-	m.Set("gauge_current_connnections", &s.curClients)
-	m.Set("gauge_current_home_connnections", &s.curHomeClients)
+	m.Set("gauge_current_connections", &s.curClients)
+	m.Set("gauge_current_home_connections", &s.curHomeClients)
 	m.Set("gauge_clients_total", expvar.Func(func() interface{} { return len(s.clientsMesh) }))
 	m.Set("gauge_clients_local", expvar.Func(func() interface{} { return len(s.clients) }))
 	m.Set("gauge_clients_remote", expvar.Func(func() interface{} { return len(s.clientsMesh) - len(s.clients) }))