mutate_each() and summarise_each() are deprecated in favour of
the new across() function that works within summarise() and mutate().
summarise_each(tbl, funs, ...)
summarise_each_(tbl, funs, vars)
mutate_each(tbl, funs, ...)
mutate_each_(tbl, funs, vars)
summarize_each(tbl, funs, ...)
summarize_each_(tbl, funs, vars)