fix(types): The second parameter of EventSource is optional (#3106)

test/types/event-source-d.ts

@@ -0,0 +1,20 @@
+import { URL } from 'url'
+import { expectType } from 'tsd'
+
+import {
+	EventSource,
+} from '../../'
+
+declare const eventSource: EventSource
+
+expectType<() => void>(eventSource.close)
+expectType<string>(eventSource.url)
+expectType<boolean>(eventSource.withCredentials)
+expectType<0 | 1 | 2>(eventSource.readyState)
+
+expectType<EventSource>(new EventSource('https://example.com'))
+expectType<EventSource>(new EventSource(new URL('https://example.com')))
+expectType<EventSource>(new EventSource('https://example.com', {}))
+expectType<EventSource>(new EventSource('https://example.com', {
+	withCredentials: true,
+}))

types/eventsource.d.ts

@@ -50,7 +50,7 @@ interface EventSource extends EventTarget {
 
 export declare const EventSource: {
   prototype: EventSource
-  new (url: string | URL, init: EventSourceInit): EventSource
+  new (url: string | URL, init?: EventSourceInit): EventSource
   readonly CLOSED: 2
   readonly CONNECTING: 0
   readonly OPEN: 1