fix for D3 bug
fix for D3 bug

https://github.com/mbostock/d3/issues/1535

bmesuere/uni-test,bmesuere/uni-test,unipept/unipept,unipept/unipept,bmesuere/uni-test,bmesuere/uni-test,unipept/unipept,bmesuere/uni-test,unipept/unipept,unipept/unipept