FIXED: Flutter CocoaPods could not find compatible versions for pod

Fixing Flutter:
CocoaPods could not find compatible versions for pod "Firebase/Firestore":
Firebase/Firestore (= 10.9.0)

In Podfile:
cloud_firestore (from `.symlinks/plugins/cloud_firestore/ios`) was resolved to 4.10.0, which depends on
Firebase/Firestore (= 10.15.0)

You have either:
* out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.
* changed the constraints of dependency `Firebase/Firestore` inside your development pod `cloud_firestore`.
You should run `pod update Firebase/Firestore` to apply changes you've made.