Master crashes on scatter_matrix
#### Code Sample, a copy-pastable example if possible

```
# Taken from the documentation (visualization.rst)
import pandas as pd
import numpy as np
df = pd.DataFrame(np.random.randn(1000, 4), columns=['a', 'b', 'c', 'd'])
pd.plotting.scatter_matrix(df, alpha=0.2, figsize=(6, 6), diagonal='kde')
```
#### Problem description

The example for `scatter_matrix` causes a crash. Removing the keywords and calling `pd.plotting.scatter_matrix(df)` also causes a crash. Works fine on 0.23.4 though.

#### Expected Output

A graph

#### Actual Output
```
2018-11-19 16:40:16.205 python[5427:142785] -[NSApplication _setup:]: unrecognized selector sent to instance 0x7ff432858630
2018-11-19 16:40:16.207 python[5427:142785] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSApplication _setup:]: unrecognized selector sent to instance 0x7ff432858630'
*** First throw call stack:
(
	0   CoreFoundation                      0x00007fff3d83b571 __exceptionPreprocess + 256
	1   libobjc.A.dylib                     0x00007fff697edefb objc_exception_throw + 48
	2   CoreFoundation                      0x00007fff3d8b8ca5 -[NSObject(NSObject) __retain_OA] + 0
	3   CoreFoundation                      0x00007fff3d7da7fe ___forwarding___ + 1468
	4   CoreFoundation                      0x00007fff3d7da1b8 _CF_forwarding_prep_0 + 120
	5   libtk8.6.dylib                      0x000000011b4b931d TkpInit + 413
	6   libtk8.6.dylib                      0x000000011b41117e Initialize + 2622
	7   _tkinter.cpython-36m-darwin.so      0x000000011b239a16 _tkinter_create + 1174
	8   python                              0x0000000106489088 _PyCFunction_FastCallDict + 200
	9   python                              0x000000010655ff4f call_function + 143
	...lines omitted for brevity...
	47  python                              0x00000001065d0122 Py_Main + 4690
	48  python                              0x00000001063ff929 main + 313
	49  libdyld.dylib                       0x00007fff6a8b4085 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
Abort trap: 6
```

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

<details>

No module named 'dask'

INSTALLED VERSIONS
------------------
commit: deb7b4d5003b939f47e525bcdaceeea48622a73a
python: 3.6.7.final.0
python-bits: 64
OS: Darwin
OS-release: 18.0.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_CA.UTF-8
LOCALE: en_CA.UTF-8

pandas: 0.24.0.dev0+1057.gdeb7b4d50
pytest: 3.9.3
pip: 10.0.1
setuptools: 40.5.0
Cython: 0.29
numpy: 1.15.3
scipy: 1.1.0
pyarrow: 0.11.1
xarray: 0.10.9
IPython: 7.1.1
sphinx: 1.8.1
patsy: 0.5.0
dateutil: 2.7.5
pytz: 2018.7
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.8
feather: None
matplotlib: 3.0.1
openpyxl: 2.5.9
xlrd: 1.1.0
xlwt: 1.2.0
xlsxwriter: 1.1.2
lxml: 4.2.5
bs4: 4.6.3
html5lib: 1.0.1
sqlalchemy: 1.2.12
pymysql: 0.9.2
psycopg2: None
jinja2: 2.10
s3fs: 0.1.6
fastparquet: 0.1.6
pandas_gbq: None
pandas_datareader: None
gcsfs: 0.1.2

</details>
