Update heatmap docstring to include x and y.
Update heatmap docstring to include x and y.

philippjfr/bokeh,KasperPRasmussen/bokeh,stonebig/bokeh,phobson/bokeh,quasiben/bokeh,bokeh/bokeh,rs2/bokeh,rs2/bokeh,KasperPRasmussen/bokeh,KasperPRasmussen/bokeh,phobson/bokeh,KasperPRasmussen/bokeh,clairetang6/bokeh,timsnyder/bokeh,justacec/bokeh,clairetang6/bokeh,ptitjano/bokeh,aavanian/bokeh,azjps/bokeh,mindriot101/bokeh,philippjfr/bokeh,ericmjl/bokeh,schoolie/bokeh,Karel-van-de-Plassche/bokeh,aiguofer/bokeh,aavanian/bokeh,phobson/bokeh,Karel-van-de-Plassche/bokeh,justacec/bokeh,jakirkham/bokeh,DuCorey/bokeh,ericmjl/bokeh,timsnyder/bokeh,ptitjano/bokeh,jakirkham/bokeh,mindriot101/bokeh,percyfal/bokeh,DuCorey/bokeh,bokeh/bokeh,draperjames/bokeh,rs2/bokeh,percyfal/bokeh,DuCorey/bokeh,philippjfr/bokeh,jakirkham/bokeh,Karel-van-de-Plassche/bokeh,azjps/bokeh,dennisobrien/bokeh,phobson/bokeh,Karel-van-de-Plassche/bokeh,mindriot101/bokeh,ptitjano/bokeh,ptitjano/bokeh,aiguofer/bokeh,timsnyder/bokeh,DuCorey/bokeh,stonebig/bokeh,percyfal/bokeh,justacec/bokeh,azjps/bokeh,schoolie/bokeh,phobson/bokeh,aiguofer/bokeh,rs2/bokeh,bokeh/bokeh,clairetang6/bokeh,stonebig/bokeh,aavanian/bokeh,justacec/bokeh,draperjames/bokeh,percyfal/bokeh,dennisobrien/bokeh,msarahan/bokeh,aavanian/bokeh,ericmjl/bokeh,jakirkham/bokeh,timsnyder/bokeh,msarahan/bokeh,azjps/bokeh,draperjames/bokeh,ericmjl/bokeh,mindriot101/bokeh,timsnyder/bokeh,KasperPRasmussen/bokeh,aavanian/bokeh,jakirkham/bokeh,DuCorey/bokeh,ericmjl/bokeh,ptitjano/bokeh,clairetang6/bokeh,dennisobrien/bokeh,schoolie/bokeh,aiguofer/bokeh,philippjfr/bokeh,msarahan/bokeh,philippjfr/bokeh,msarahan/bokeh,dennisobrien/bokeh,stonebig/bokeh,schoolie/bokeh,draperjames/bokeh,rs2/bokeh,dennisobrien/bokeh,azjps/bokeh,aiguofer/bokeh,percyfal/bokeh,bokeh/bokeh,schoolie/bokeh,bokeh/bokeh,quasiben/bokeh,Karel-van-de-Plassche/bokeh,draperjames/bokeh,quasiben/bokeh