[fix]Firewake Sliver ability to boost can target non-sliver

[Aswan jaguar]

Describe the Bug:
Firewake Sliver ability to boost can target non-sliver creatures a face down creature in my case.

Which card did behave improperly?
Firewake Sliver

Which update are you using? (date, name)Which type? (duel, gauntlet, sealed deck)
Manalink dev 778ccb5 version - duel

What exactly should be the correct behavior/interaction?
Firewake Sliver: All Slivers have "1, Sacrifice this permanent: Target Sliver creature gets +2/+2 until end of turn."

Are any other cards possibly affected by this bug?
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[Aswan jaguar]

Fixed in commit 5cb513a4.