docs: fix variable assignment mistake on example code

[sryoya]

Related issue

none.
As this has just minor changes, I created this PR without a prior discussion.

Proposed changes

Fixed wrong variable-assignment statements in the example codes, which would make a compiler complain if they were on .go files 😄

Checklist

• I have read the contributing guidelines and signed the CLA.
• 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 green light (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 necessary documentation within the code base (if appropriate).

Further comments

none

[aeneasr]

Awesome 🎉

Thank you for your contribution!