[Bug]: Y-axis unit labeling does not update when zooming in/out #1142

Bug description

In a chart with high peaks, e.g. for network traffic into the gigabits per second, zooming into an area with much lower values (e.g. low megabits per second), while the ticks on the y-axis change, the unit label does not. Only when clicking the tiny Netdata logo to update the chart, the unit is updated, too.

Expected behavior

Update the label along with the ticks.

Steps to reproduce

1. See above

Screenshots

Error Logs

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Desktop

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Additional context

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