Share schema to solve following error:

  xcodebuild: error: The project 'protobuf-ios' does not contain a scheme named 'protobuf-ios'.

Ensure the schemes of your target are Shared. This option makes a scheme visible to anyone using that project. To enable
it, go to the menu: Product > Scheme > Manage Schemes.

see http://ioscowboy.com/2013/06/09/travis-and-ios-projects.html