[ensure-up-to-date] fix path in error message

[grokify]

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
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Description of the PR

Update ensure-up-to-date script path in script error message so it matches new path in bin/utils (vs. bin).

[jmini]

Thank you a lot for this small change.