Add iOS device arch to Cronet framework binary build 

Looks like our existing [CronetFramework](https://cocoapods.org/pods/CronetFramework) pod only contains x86_64 and i386 but are missing device archs (arm64, armv7).  This one tracks adding the missing archs to the pod 

```bash 
$ lipo -info Cronet 
Architectures in the fat file: Cronet are: x86_64 i386 
``` 