Firstly, thanks for this plugin - it looks great!

Apologies if this isn't the case, but I think that the graph is inaccessible to screen reader users and other users of assistive tech since, as far as I can tell, the graph is made up of a series of <div> elements. Would you consider reworking how the graphs are drawn, so that the information that the graphs are trying to convey are also accessible to users of assistive technologies?

This may or may not help, but Adrian Roselli wrote up a great piece on accessibility issues with GitHub's contributions graph. GitHub have since made some accessibility improvements. One of the changes they made was switching the graph from using an SVG to a <table>.