Fix audit online release variable

[Moisan]

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#7685 changed the release variable but not the following lines leading to this error currently when using brew audit --online:

Error: undefined local variable or method `release' for #<Homebrew::FormulaAuditor:0x00007fb5c7b89a28>

[MikeMcQuaid]

Oops! The @ was a typo here; I've suggested I think a slightly better fix.

[Bo98]

Thanks!