Update server.rst: wrong apache module name (#8427)
Update server.rst: wrong apache module name (#8427)

In section about Apache reverse proxy there was a wrong module name: `http_proxy` changed to `proxy_http`.
ericmjl/bokeh,stonebig/bokeh,ericmjl/bokeh,bokeh/bokeh,timsnyder/bokeh,stonebig/bokeh,timsnyder/bokeh,stonebig/bokeh,bokeh/bokeh,timsnyder/bokeh,stonebig/bokeh,ericmjl/bokeh,bokeh/bokeh,ericmjl/bokeh,bokeh/bokeh,ericmjl/bokeh,timsnyder/bokeh,bokeh/bokeh,timsnyder/bokeh