build.tt: Fix reference to build.ischannel.

It's actually lower-case despite the spelling in the SQL file(s), because the schema auto-generator from DBIx::Class doesn't take it into account because it's working on SQLite and the latter seems to ignore case.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

Created by  aszlig  on April 26, 2015
CHKVSGZGGPIFXFKRHQU4QMEXHJXQMMCRQCY3S5YA4S4JKFLXAAVAC
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