example: changed 403 to 401(not authorized)

[oslook]

Thank you very much for the examples. It's very helpful.

I encountered some in using the provided example program. The example of singleton filter's command of the test after checking the example code. The command prompted in the document is not very prepared.

like: curl localhost:8080/ -H "x-auth: foo"

In order to avoid other person ambiguity, I made some modifications to make it clearer and more accurate.

[solo-build-bot[bot]]

Waiting for approval from someone in the solo-io org to start testing.

[yuval-k]

thank you for fixing!