Update ekka to version 0.15.8, mria to version 0.15.8, and optvar to 1.0.5.
This fixes occasional assertion failures:
`{{badmatch,noproc},[{optvar,read,2,[{file,"optvar.erl"},{line,140}]},{optvar,read,1,[{file,"optvar.erl"},{line,124}]},...`