cmd/update-report: fix output of new casks

[miccal]

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In a recent PR I added an output for "New Casks" to brew update, like so:

==> New Casks
a_shiny_new_cask

However, after merging I noticed that the output was actually being shown as follows:

==> New Casks
homebrew/cask/a_shiny_new_cask

This trivial change fixes this oversight.

Apologies for missing this in my original PR.

Thank you.

[MikeMcQuaid]

Thanks again @miccal!

[miccal]

No problem @MikeMcQuaid, sorry for the silly error on my part.

[MikeMcQuaid]

@miccal I'll accept your apology when you're made more than me (which will take you a long time) 😂