Fix the build of the Swift Package with Xcode 12.5 beta 1 (#983)

Author: layoutSubviews

Segment/Internal/SEGIntegrationsManager.m

@@ -6,6 +6,7 @@
 //  Copyright © 2016 Segment. All rights reserved.
 //
 
+@import Foundation;
 #if TARGET_OS_IPHONE
 @import UIKit;
 #endif