Fix truth table in Exercise 6.3

[JohnChen0]

Fixing typos in the truth table in the answer to Exercise 6.3.

[aless73]

qt.sigmay() * ket0 yields [[0.+0.j] [0.+1.j]] which is equal to 1j * ket1
qt.sigmay() * ket1 yields [[0.-1.j] [0.+0.j]] which is equal to -1j * ket0
therefore the first two lines of the truth table should be fixed as follows:
input: |0⟩ output: 𝑖|1⟩
input: |1⟩ output: −𝑖|0⟩