swift - Protobuf is getting installed without mentioning it in pod file -

i running odd problem swift project. below pod file. using swift 3. when run pod install, end seeing

installing protobuf (3.2.0) 

now don't have pod mentioned anywhere in pod file. why getting installed ? framework causes 200+ warnings swift 3 , project works without ( delete scheme), want find out coming , delete it.

# platform :ios, '10.0'  target 'randomapp'     use_frameworks!         pod 'firebase'        pod 'firebase/auth'        pod 'firebase/database'        pod 'firebase/messaging'        pod 'firebase/core'         pod 'firebase/storage'         pod 'mrprogress'         pod 'reachability'  end 

some other framework you're using using dependancy.