fix educators links in book.yaml (#3465)
fix educators links in book.yaml (#3465)

Fix educators links in book.yaml. 

This breaks devsite staging currently.
quantumlib/Cirq,balopat/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,quantumlib/Cirq,balopat/Cirq,balopat/Cirq