plotting dtype "UInt32" fails
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd

s = pd.Series([ 4, 5, 3 ,2 ], dtype="UInt32")
s.astype("int32").plot() # succeeds
s.plot() # fails


```
fails with
```
Traceback (most recent call last):
  File "test_plot.py", line 7, in <module>
    s.plot()
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 2740, in __call__
    **kwds)
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 1995, in plot_series
    **kwds)
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 1798, in _plot
    plot_obj.generate()
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 251, in generate
    self._make_plot()
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 993, in _make_plot
    **kwds)
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 1008, in _plot
    lines = MPLPlot._plot(ax, x, y_values, style=style, **kwds)
  File "/nix/store/biq309lxqwpl1nfap4h3s58wcxd134xq-python3.7-pandas-0.24.1/lib/python3.7/site-packages/pandas/plotting/_core.py", line 598, in _plot
    return ax.plot(*args, **kwds)
  File "/nix/store/xgfsbxa29szyi30hl48hac1gihic3z3f-python3.7-matplotlib-3.0.3/lib/python3.7/site-packages/matplotlib/__init__.py", line 1810, in inner
    return func(ax, *args, **kwargs)
  File "/nix/store/xgfsbxa29szyi30hl48hac1gihic3z3f-python3.7-matplotlib-3.0.3/lib/python3.7/site-packages/matplotlib/axes/_axes.py", line 1611, in plot
    for line in self._get_lines(*args, **kwargs):
  File "/nix/store/xgfsbxa29szyi30hl48hac1gihic3z3f-python3.7-matplotlib-3.0.3/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 393, in _grab_next_args
    yield from self._plot_args(this, kwargs)
  File "/nix/store/xgfsbxa29szyi30hl48hac1gihic3z3f-python3.7-matplotlib-3.0.3/lib/python3.7/site-packages/matplotlib/axes/_base.py", line 378, in _plot_args
    ncx, ncy = x.shape[1], y.shape[1]
IndexError: tuple index out of range
```


#### Problem description
When using the new type UInt32, plotting won't work.

#### Output of ``pd.show_versions()``

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.2.final.0
python-bits: 64
OS: Linux
OS-release: 4.20.12
machine: x86_64
processor: 
byteorder: little
LC_ALL: None
LANG: C.UTF-8
LOCALE: None.None

pandas: 0+unknown
pytest: None
pip: 19.0.3
setuptools: 40.8.0
Cython: None
numpy: 1.16.1
scipy: 1.2.1
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.8.0
pytz: 2018.9
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.9
feather: None
matplotlib: 3.0.3
openpyxl: 2.6.0
xlrd: 1.2.0
xlwt: 1.3.0
xlsxwriter: None
lxml.etree: 4.3.1
bs4: 4.7.1
html5lib: 1.0.1
sqlalchemy: 1.2.14
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None

</details>
