Updated nyc_taxi

[jbednar]

Updated the nyc_taxi example:

• Updated to current versions of HoloViz tools
• Fixed AttributeError: 'Dataset' object has no attribute 'Count' #144 ; needed updating to match changes in HoloViews datashader support
• Switched away from broken tile sources (worked fine locally, but not on examples.pyviz.org or other deployments)
• Removed distracting ds.count('passenger_count') - confusingly seems to count the total passengers, but really only counts the number of records where that field is not missing
• Replaced ancient Hot colormap with colorcet.fire; Hot was better than other hot versions, but still not properly uniform
• Updated notebook and dashboard to use rasterize now that they are well supported in Bokeh

To do:

• Should update to Datashader 0.13 when released to get the dynspread fixes.
• Update last cell of nyc_taxi-nongeo.ipynb; currently breaks with error "No plotting class for Dataset found".
• Fix anaconda-project.yml to avoid dependencies/packages issue
• When above are done, run anaconda-project lock and update the nyc_taxi/anaconda-project-lock.yml file

[github-actions]

Your changes were successfully integrated in the dev site, make sure to review
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[github-actions]

Your changes were successfully integrated in the dev site, make sure to review
the pages of the projects you touched before merging this PR: https://holoviz-dev.github.io/examples/.
You can also download an archive of the site from the workflow summary page which comes in handy
when your dev site built was overriden by another PR (we have a single dev site!).