Fix KeyboardManager marked as unavailable in extensions

Author: nathantannar4

Sources/KeyboardManager/KeyboardManager.swift

@@ -28,7 +28,6 @@
 import UIKit
 
 /// An object that observes keyboard notifications such that event callbacks can be set for each notification
-@available(iOSApplicationExtension, unavailable)
 open class KeyboardManager: NSObject, UIGestureRecognizerDelegate {
 
     /// A callback that passes a `KeyboardNotification` as an input