c94eae breaks the test
the commit <Add Indent Support in to_json (#28130)> breaks the test. `pytest pandas/tests/io/json/test_pandas.py`.

![image](https://user-images.githubusercontent.com/19762154/65853170-915d0180-e393-11e9-9d1a-38ad3713e145.png)


![image](https://user-images.githubusercontent.com/19762154/65853052-2f040100-e393-11e9-8155-fca3d69e0f3a.png)

<details>

/Users/donghojung/anaconda3/envs/pandas-dev/lib/python3.7/site-packages/xarray/core/merge.py:17: FutureWarning: The Panel class is removed from pandas. Accessing it from the top-level namespace will also be removed in the next version
  PANDAS_TYPES = (pd.Series, pd.DataFrame, pd.Panel)

INSTALLED VERSIONS
------------------
commit           : c94eaeec0387eb61eff303c24fc5ada24e1c563c
python           : 3.7.4.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 18.7.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : en_US.UTF-8
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.26.0.dev0+376.gc94eaeec0
numpy            : 1.16.5
pytz             : 2019.2
dateutil         : 2.8.0
pip              : 19.2.2
setuptools       : 41.0.1
Cython           : 0.29.13
pytest           : 5.0.1
hypothesis       : 4.32.2
sphinx           : 1.8.5
blosc            : None
feather          : None
xlsxwriter       : 1.1.8
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.8.0
pandas_datareader: None
bs4              : 4.8.0
bottleneck       : 1.2.1
fastparquet      : 0.3.0
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : 3.1.1
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 2.6.2
pandas_gbq       : None
pyarrow          : 0.13.0
pytables         : None
s3fs             : 0.2.1
scipy            : 1.3.1
sqlalchemy       : 1.3.7
tables           : 3.5.2
xarray           : 0.12.1
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.1.8

</details>
