How To Reproduce

1. Clone this repo, you shouldn have no Pods folder in your local repo for it's ignored by git
2. Do pod install and nothing change (or may only change task hash ID of [CP] Copy Pods Resources). Compile project and all goes well.
3. Do pod install again, and new changes appear on BuildFailExample.xcodeproj/project.pbxproj. [CP] Copy Pods Resources build phase script is removed and project will fail to build because Firebase.h can not be found in its modulemap.
4. This is because that Original Firebase header in Pods/Firebase/CoreOnly/Source/Firebase.h is removed during second pod install
5. Clear all Pods folder by rm -rf Pods , and then you go back to step 1.