Update run-hop-in-apache-airflow.adoc

[dmainou]

on the front end the underscores being changed don't show up for the first 2 instances but do for the 3rd.

Turns out the variable had double underscores on the first 2 instances and not on the 3rd (which displays correctly on the front end)

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[bamaer]

thanks a lot for the PR, Diego. the double underscores are what Airflow expects, so can't be reduced to a single one...
closing the PR, but appreciate the contribution nevertheless!