Mirrored left hand tick labels still allocates unused spaces for labels

[tomduncalf]

When setting mirror: true for y-axis ticks, a blank space is left where the labels would have been if they were not mirrored. I would expect the first grid line to be flush to the left hand edge of the canvas in this situation, as the space is not needed.

Test case: http://jsbin.com/xeludekodu/1/edit?html,js,output

[tomduncalf]

Thanks!