Add missing "error" event to on and off type definitions

relay.ts

@@ -3,6 +3,8 @@
 import {Event, verifySignature, validateEvent} from './event'
 import {Filter, matchFilters} from './filter'
 
+type RelayEvent = 'connect' | 'disconnect' | 'error' | 'notice'
+
 export type Relay = {
   url: string
   status: number
@@ -10,8 +12,8 @@ export type Relay = {
   close: () => Promise<void>
   sub: (filters: Filter[], opts: SubscriptionOptions) => Sub
   publish: (event: Event) => Pub
-  on: (type: 'connect' | 'disconnect' | 'notice', cb: any) => void
-  off: (type: 'connect' | 'disconnect' | 'notice', cb: any) => void
+  on: (type: RelayEvent, cb: any) => void
+  off: (type: RelayEvent, cb: any) => void
 }
 export type Pub = {
   on: (type: 'ok' | 'seen' | 'failed', cb: any) => void
@@ -185,7 +187,7 @@ export function relayInit(url: string): Relay {
     url,
     sub,
     on: (
-      type: 'connect' | 'disconnect' | 'error' | 'notice',
+      type: RelayEvent,
       cb: any
     ): void => {
       listeners[type].push(cb)
@@ -194,7 +196,7 @@ export function relayInit(url: string): Relay {
       }
     },
     off: (
-      type: 'connect' | 'disconnect' | 'error' | 'notice',
+      type: RelayEvent,
       cb: any
     ): void => {
       let index = listeners[type].indexOf(cb)