update calibration example to use a monophyletic constraint
update calibration example to use a monophyletic constraint

tgvaughan/beast2,Anaphory/beast2,CompEvol/beast2,tgvaughan/beast2,CompEvol/beast2,tgvaughan/beast2,Anaphory/beast2,Anaphory/beast2,Anaphory/beast2,tgvaughan/beast2,CompEvol/beast2,CompEvol/beast2