Podspec: The minimal iOS platform should be iOS 9.0

[manuroe]

Running this pod within in app on an iOS8 makes the app crash.

The reason is that the framework uses AVCaptureSessionInterruptionReasonKey which is available since iOS 9.0.

Crash log:

- Dyld Error Message:
  Symbol not found: _AVCaptureSessionInterruptionReasonKey
  Referenced from: /private/var/mobile/Containers/Bundle/Application/XXXX/Yyyy.app/Frameworks/WebRTC.framework/WebRTC (which was built for iOS 9.0)
  Expected in: /System/Library/Frameworks/AVFoundation.framework/AVFoundation
 in /private/var/mobile/Containers/Bundle/Application/XXXX/Yyyy.app/Frameworks/WebRTC.framework/WebRTC
  Dyld Version: 353.12

[AlexKMDev]

Thanks. You should report this to official bug tracker too, because I'm just building this library from provided sources. Will change podspec soon to use iOS 9.