DOC: inconsistency in doc argument types
This is not exactly right, but we have an inconsitency in the argument specifications of using 'array_like' vs 'array-like', in argument types we should settle on one (prob 'array-like')

```
(pandas-dev) ~/pandas$ grep -r array-like --include '*.py' pandas|wc
     317    2259   24072
(pandas-dev) ~/pandas$ grep -r array_like --include '*.py' pandas|wc
     104     498    7414
```

Similar to this
```
pandas/plotting/_core.py:    yerr : DataFrame, Series, array-like, dict and str
```