fix: oauth2-client get client: fix example --json option

[kangaechu]

The --json option does not exist in the current version of hydra. The --format json option had been added in place of the --json option. However, the --json option was left in the example. So, I fixed it.

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #3497 (3decda3) into master (cf20054) will not change coverage.
The diff coverage is 100.00%.

❗ Current head 3decda3 differs from pull request most recent head 3236557. Consider uploading reports for the commit 3236557 to get more accurate results

@@           Coverage Diff           @@
##           master    #3497   +/-   ##
=======================================
  Coverage   76.87%   76.87%           
=======================================
  Files         124      124           
  Lines        9175     9175           
=======================================
  Hits         7053     7053           
  Misses       1673     1673           
  Partials      449      449           

Impacted Files	Coverage Δ
cmd/cmd_get_client.go	83.33% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[aeneasr]

Awesome, thank you! 🎉 Your contribution makes Ory better :)