fix: Fixed typo preventing finding a free key slot when attaching a key

Author: mrfigg

lib/page.js

@@ -700,7 +700,7 @@ class Page extends EventEmitter {
 
       index = -1
 
-      for (const i = 0; i < this.KEY_COUNT; i++) {
+      for (let i = 0; i < this.KEY_COUNT; i++) {
         if (!this._keys.has(i)) {
           index = i