fix moment-utils startOfDay, endOfDay
fix moment-utils startOfDay, endOfDay

The two methods in moment-utils invoke moment().startOf and
moment().endOf which mutate the original value. The call to clone() has
to be added in order to prevent that.

dmtrKovalenko/material-ui-pickers,mbrookes/material-ui,oliviertassinari/material-ui,mui-org/material-ui,mui-org/material-ui,callemall/material-ui,oliviertassinari/material-ui,oliviertassinari/material-ui,rscnt/material-ui,rscnt/material-ui,callemall/material-ui,mbrookes/material-ui,rscnt/material-ui,callemall/material-ui,mui-org/material-ui,callemall/material-ui,dmtrKovalenko/material-ui-pickers,mbrookes/material-ui