GlSurface is_single_buffered implementation for EGL is backwards

[royaltm]

The function reports true for double buffered and false for single buffered. Should be the opposite.

glutin/glutin/src/api/egl/surface.rs

Line 331 in 8e0960d

fn is_single_buffered(&self) -> bool {

    fn is_single_buffered(&self) -> bool {
        unsafe { self.raw_attribute(egl::RENDER_BUFFER as EGLint) != egl::SINGLE_BUFFER as i32 }
    }

should be == egl::SINGLE_BUFFER