some size optimizations (#69)

* -4 bytes optimization

* -16 bytes optimization

---------

Co-authored-by: Igor Mitusov <igi.sev@gmail.com>

index.js

@@ -1,13 +1,12 @@
 export let createNanoEvents = () => ({
   emit(event, ...args) {
-    let callbacks = this.events[event] || []
-    for (let i = 0, length = callbacks.length; i < length; i++) {
+    for (let i = 0, callbacks = this.events[event] || [], length = callbacks.length; i < length; i++) {
       callbacks[i](...args)
     }
   },
   events: {},
   on(event, cb) {
-    this.events[event]?.push(cb) || (this.events[event] = [cb])
+    (this.events[event]||=[]).push(cb);
     return () => {
       this.events[event] = this.events[event]?.filter(i => cb !== i)
     }