make nanops work when ndim==1 and axis==0 ( issue #7354 )
This fixes issue #7354, where some `nanops` functions fail for 1-dimensional arrays for the argument `axis=0`.

as an aside do you test for invalid axis (>ndim)
 No, currently there is no exception testing.
 ok easy enough to add assert statements inline - when u have a chance
 The travis build is passing and the pull request should be up-to-date, so this should be ready to merge.
 merged via https://github.com/pydata/pandas/commit/586e3173cce75373f9bf395d9c0709c67613956a

thanks!
