Resize doesn't accept id string

[alexcjohnson]

dynamic sizing requires you to explicitly attach a resize handler:

window.onresize = function() { Plotly.Plots.resize(gd); };

This works fine if you pass the plot div element gd, but (unlike the rest of the API) you cannot use an id 'myGraph' or you'll get an error:

Uncaught (in promise) TypeError:
  Failed to execute 'getComputedStyle' on 'Window': parameter 1 is not of type 'Element'.

cc @VeraZab

[alexcjohnson]

closed by #2212