Fix error message from cirq.final_wavefunction to cirq.final_density_matrix #2778 (#2844)
Fix error message from cirq.final_wavefunction to cirq.final_density_matrix #2778 (#2844)

Error message changes for  cirq/sim/mux.py

From:-
"Maybe you wanted `cirq.final_wavefunction`
To:-
"Maybe you wanted `cirq.final_density_matrix`? "

Fixes: https://github.com/quantumlib/Cirq/issues/2778
quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,balopat/Cirq,balopat/Cirq