gloss-examples.cabal: fix typo in 'Build-depends:' field

Noticed by Cabal:

> Warning: gloss-examples.cabal: Unexpected section 'build-depends' on line 284
> Warning: gloss-examples.cabal: Unexpected section 'build-depends' on line 299
> Warning: gloss-examples.cabal: Unexpected section 'build-depends' on line 317

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>