nemenyi function fails with non-matrix objects

If a user works with a data.frame / data.table / tibble, then the function would fail with an error:
> Error in friedman.test.default(data) : 
>  argument "groups" is missing, with no default

This is because `friedman.test` method is used instead of just a function in that case.

A fix for the time being is to do:
```
nemenyi(as.matrix(ourTable))
```