arvo: fix hoon source reference in +boot re-compilation
[raw cop]
=/ hot
~> %slog.[0 leaf+"vega: recompiling hoon %{<`@`nex>}"]
- (road |.((slum cop [%noun hun])))
+ (road |.((slum cop [%noun u.hun])))
[hot .*(0 +.hot)]
:: extract the hoon core from the outer gate (+ride)
::
