Flip function not working well

[raphamorim]

Doesn't work well

.flip('horizontal')
.image('images/person.jpg', 0, 0, 200, 200)
.flipEnd()
.image('images/person.jpg', 0, 250, 200, 200)

Doesn't work well

.flip('vertical')

I think it's have some relationship with another issue #3

[raphamorim]

Ref: a8b9476