Travis: Exclude CMake .pc files
Travis: Exclude CMake .pc files

Exclude the unconfigured .pc input files of the CMake
based install: they shall not be packed/distributed,
only their outputs are

google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf,google/protobuf