fix sample-(neg-)binomial mangling arguments

was:

    => (sample-binomial 10) ; expect a seq of 10 0's and 1's
    1
    => (sample-binomial 1 :size 10) ; expect a single number between 0 and 10
    (4 9 5 7 4 8 4 6 6 6)

is:

    => (sample-binomial 10)
    (1 1 1 0 0 1 0 0 1 1)
    => (sample-binomial 1 :size 10)
    6

see also https://github.com/liebke/incanter/pull/109