The layout engine cannot be changed between two graph renderings

[magjac]

If an attempt to change the layout engine is made after rendering the first graph, d3-graphviz throws Error: Too late to change engine.

Although this implementation was intentional and aimed at informing the user that a change of the layout engine between a call to graphviz.dot and graphviz.render had no effect, it was a bad idea since it prohibits transitions between two graphs rendered with different layout engines.

Rather than throwing an error, such a change should be allowed and its effect properly documented.