Typo: ussuance --> issuance

[elfahxh]

Typo: ussuance --> issuance

[Artemkaaas]

@elfahxh Thank you for the contribution!
However, it cannot be accepted without a sign-off from you about intellectual property.
Please see https://github.com/probot/dco#how-it-works and instruction about how to fix it: https://github.com/hyperledger/indy-sdk/blob/master/docs/contributors/signing-commits.md#how-to-sign-previous-commits

[jovfer]

@elfahxh I'm closing this PR due to inactivity. Fill free to re-open it as soon as you will have time to fix DCO check.