Fix deprecated call to datetime64 for NP_EPOCH. (#6192)
Fix deprecated call to datetime64 for NP_EPOCH. (#6192)

* Fix deprecated call to datetime64 for NP_EPOCH.

* Switch to ms, make private.

schoolie/bokeh,philippjfr/bokeh,stonebig/bokeh,percyfal/bokeh,DuCorey/bokeh,jakirkham/bokeh,aavanian/bokeh,mindriot101/bokeh,mindriot101/bokeh,dennisobrien/bokeh,dennisobrien/bokeh,rs2/bokeh,stonebig/bokeh,bokeh/bokeh,bokeh/bokeh,percyfal/bokeh,philippjfr/bokeh,DuCorey/bokeh,jakirkham/bokeh,bokeh/bokeh,DuCorey/bokeh,bokeh/bokeh,ericmjl/bokeh,Karel-van-de-Plassche/bokeh,dennisobrien/bokeh,rs2/bokeh,Karel-van-de-Plassche/bokeh,timsnyder/bokeh,aavanian/bokeh,schoolie/bokeh,jakirkham/bokeh,dennisobrien/bokeh,timsnyder/bokeh,rs2/bokeh,stonebig/bokeh,aavanian/bokeh,stonebig/bokeh,Karel-van-de-Plassche/bokeh,dennisobrien/bokeh,ericmjl/bokeh,aavanian/bokeh,mindriot101/bokeh,philippjfr/bokeh,ericmjl/bokeh,rs2/bokeh,DuCorey/bokeh,DuCorey/bokeh,percyfal/bokeh,mindriot101/bokeh,jakirkham/bokeh,Karel-van-de-Plassche/bokeh,Karel-van-de-Plassche/bokeh,schoolie/bokeh,bokeh/bokeh,percyfal/bokeh,rs2/bokeh,philippjfr/bokeh,schoolie/bokeh,philippjfr/bokeh,aavanian/bokeh,timsnyder/bokeh,ericmjl/bokeh,timsnyder/bokeh,timsnyder/bokeh,ericmjl/bokeh,schoolie/bokeh,jakirkham/bokeh,percyfal/bokeh