IOS ARCore dependency update

[dnkoulouris]

Build fails with dependency constraint error, due to today's upgrades in Firebase libraries.

If I run pod install in my project, I get:

[!] CocoaPods could not find compatible versions for pod "Firebase/CoreOnly":
In Podfile:
ar_flutter_plugin (from .symlinks/plugins/ar_flutter_plugin/ios) was resolved to 0.6.2, which depends on
ARCore/CloudAnchors (> 1.26.0) was resolved to 1.26.0, which depends on
Firebase/RemoteConfig (> 8.0) was resolved to 8.0.0, which depends on
Firebase/CoreOnly (= 8.0.0)

firebase_core (from `.symlinks/plugins/firebase_core/ios`) was resolved to 1.19.0, which depends on
  Firebase/CoreOnly (= 9.2.0)

Fix:
Change line 23 of ios/ar_flutter_plugin.podspec file to s.dependency 'ARCore/CloudAnchors', '~> 1.32.0'