[cairo] Documentation typos.

[Simon Sapin]

In docs for cairo_ps_surface_set_eps()

> This function should only be called before any drawing operations
> have been performed on the current page.

Shouldn’t that be "preformed on the surface" ?

Arguably the point is moot considering:

> An Encapsulated PostScript file should never contain more than one page.

But I still think this change would make the sentence less confusing.

-- 
Simon Sapin