How to change the tick format of a plotly color bar?

I plot a line track over a map using plotly. I add a scale of the used colors. Data range for the ticks are numbers between 0.... 30 000. The ticks are displayed as "5k", "10k", "15k"... instead of "5000", "10000", "15000"... How do I change the ticks format to the latter?

My code:

# Draw a plot of a ground track
import plotly.graph_objects as go

fig = go.Figure(go.Scattermapbox(
    mode = "markers",   
    lon = data.Wgs84Longitude,
    lat = data.Wgs84Latitude,
    marker = {'size': 5, 
              'color':data.Wgs84Altitude, 
              'colorscale': 'viridis', 
              'opacity': 0.5,
              'showscale': True,
              'colorbar': dict(
                  title='Altitude / m',
                  thickness=20,
                  titleside='top',
                  outlinecolor='rgba(68,68,68,0)',
                  ticks='outside',
                  ticklen=3)  }))

fig.update_layout(
    title = "Ground Track",
    title_x=0,
    title_y=0.95,
    width=800, 
    height=700,
    margin ={'l':0,'t':50,'b':0,'r':0},
    mapbox = {
        'center': {'lon': 10, 'lat': 10},
        'style': "stamen-terrain",
        'center': {'lon': Lon, 'lat': Lat},
        'zoom': 8})

fig.show()

Thank you for your help.data