[REQUIRED] Step 1: Describe your environment

• Xcode version: 11.3.1
• Firebase SDK version: 6.21.0
• Firebase Component: Core
• Component version: 6.21.0
• Installation method: Carthage

[REQUIRED] Step 2: Describe the problem

When adding Firebase v6.21.0 to your project using Carthage, a header file called "FirebaseCore-umbrella.h" is created in FirebaseCore. This will trigger a warning in Xcode, as it is not included in the header file defined in the module.modulemap of FirebaseCore.
This does not happen when using v6.19.0 of Firebase.

Warning in Xcode is: umbrella header for module 'FirebaseCore' does not include header 'FirebaseCore-umbrella.h'

Steps to reproduce:

Follow steps in Carthage.md to install setup Firebase using Carthage, by adding this line to the Carthage file:
binary "https://dl.google.com/dl/firebase/ios/carthage/FirebaseAnalyticsBinary.json" == 6.21.0