Line is diagonal if yAxis options set

If no title is set for yAxis, it behaves correctly, there is an horizontal line

But if we set a title, the line becomes diagonal:

To reproduce,

Go on https://www.chartjs.org/chartjs-plugin-annotation/master/guide/types/line.html#configuration and add in the options:

scales: {
    yAxis: {
        title: {
            display: true,
            text: "My First Dataset"
        }
    }
},

[kurkle]

I think we could improve the defaults to be the first axes in the chart, which would mean you only need to specify when more than two scales are involved. That would be a breaking change, so something to consider for v2.

[stockiNail]

I have set this issue and the PR #678 as breaking change because the x/yScaleID options defaults are changed.