chore: prep 815 release (#256)

CHANGELOG.md

@@ -1,4 +1,4 @@
-# Unreleased
+# 8.1.5
 - [fixed] Deliver App Delegate callbacks to delegates that handle them by
   forwarding rather than by implementing them, such as the one SwiftUI installs
   for `UIApplicationDelegateAdaptor`. (#247)

GoogleUtilities.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'GoogleUtilities'
-  s.version          = '8.1.4'
+  s.version          = '8.1.5'
   s.summary          = 'Google Utilities for Apple platform SDKs'
 
   s.description      = <<-DESC