examples/gogears.go: Change gl/gl20 -> gl
examples/gogears.go: Change gl/gl20 -> gl

Signed-off-by: David Aguilar <9de348c050f7cd1ca590883733c4e531ce610bf4@gmail.com>

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