try to fix https://travis-ci.org/github/grzegorzmazur/yacas/jobs/661064035
try to fix https://travis-ci.org/github/grzegorzmazur/yacas/jobs/661064035

grzegorzmazur/yacas,grzegorzmazur/yacas,grzegorzmazur/yacas,grzegorzmazur/yacas,grzegorzmazur/yacas,grzegorzmazur/yacas,grzegorzmazur/yacas