docs(nrql_alert_condition.html.markdown): fix example

[mvdiener]

Description

Update the docs to use a valid example.

Fixes #
Trying to use the previous example gives errors about invalid Handlebars. This updates the docs example to a valid Handlebars statement.

Type of change

• This change requires a documentation update

Checklist:

Please delete options that are not relevant.

• I have made corresponding changes to the documentation

How to test this change?

Only docs changes.

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}