Address Firefox warning in `deferred` example

[leod]

Firefox says the following in the deferred example, which does not bind any attributes.

WebGL warning: drawArraysInstanced: Drawing without vertex attrib 0 array enabled forces the browser to do expensive emulation work when running on desktop OpenGL platforms, for example on Mac. It is preferable to always draw with vertex attrib 0 array enabled, by using bindAttribLocation to bind some always-used attribute to location 0.