Change types for PauliString.get() (#999)
Change types for PauliString.get() (#999)

Fixes https://github.com/quantumlib/Cirq/issues/966
quantumlib/Cirq,balopat/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,balopat/Cirq,quantumlib/Cirq