Replace "prn" with "voucher".

src/_secureaccesstokenauthorizer/controller.py

src/_secureaccesstokenauthorizer/model.py

src/_secureaccesstokenauthorizer/resource.py

src/_secureaccesstokenauthorizer/tests/strategies.py

...secureaccesstokenauthorizer/tests/test_client_resource.py

src/_secureaccesstokenauthorizer/tests/test_model.py