examples/gomandel.go: Update complex constructor usage
examples/gomandel.go: Update complex constructor usage

The two-argument constructor cmplx is now spelled complex.

References: http://golang.org/doc/devel/release.html#2011-01-20
Signed-off-by: David Aguilar <9de348c050f7cd1ca590883733c4e531ce610bf4@gmail.com>

go-gl-legacy/glu,0xfaded/glu,go-gl-legacy/gl,go-gl-legacy/glu,go-gl-legacy/glu,go-gl-legacy/gl,0xfaded/glu