Error in slicing by datetime January 1, 2020
#### Code Sample, a copy-pastable example if possible

```python
import pandas as pd

dt = {'No': {pd.Timestamp('2020-01-01 00:00:00'): 123,
  pd.Timestamp('1900-01-01 00:00:00'): 345,
  pd.Timestamp('2017-04-18 00:00:00'): 946,
  pd.Timestamp('2020-01-02 00:00:00'): 940 },
 'CB': {pd.Timestamp('2020-01-01 00:00:00'): 'Sc',
  pd.Timestamp('1900-01-01 00:00:00'): 'Dr',
  pd.Timestamp('2017-04-18 00:00:00'): 'St',
  pd.Timestamp('2020-01-02 00:00:00'): 'Sc'}}

df = pd.DataFrame(dt)


# **only January 1 does not work properly**
print(df['2019-12-31':])
print(df['2020-01-01':])
print(df['2020-01-02':])


# **All work properly**
print(df[df.index >='2019-12-31'])
print(df[df.index >='2020-01-01'])
print(df[df.index >='2020-01-02'])

```
#### Problem description
Slicing by datetime index on January 1, 2020 returns the whole DataFrame

**print(df['2020-01-01':])**

Shows the whole DataFrame

#### Expected Output
# only January 1 does not work properly


**print(df['2020-01-01':])**

incorrectly shows the whole DataFrame

                   No  CB
2020-01-01  123  Sc
1900-01-01  345  Dr
2017-04-18  946  St
2020-01-02  946  Sc


**print(df['2020-01-02':])**

No  CB
2020-01-02  946  Sc


# All work properly
**print(df[df.index >='2019-12-31'])**

No  CB
2020-01-01  123  Sc
2020-01-02  946  Sc


**print(df[df.index >='2020-01-01'])**


#works properly
                     No  CB
2020-01-01  123  Sc
2020-01-02  946  Sc

**print(df[df.index >='2020-01-02'])**

                     No  CB
2020-01-01  123  Sc
2020-01-02  946  Sc


#### 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      : 32
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : Intel64 Family 6 Model 142 Stepping 9, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 1.0.3
numpy            : 1.18.2
pytz             : 2018.9
dateutil         : 2.8.0
pip              : 20.0.2
setuptools       : 40.6.2
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.10
IPython          : 7.4.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.0.3
numexpr          : None
odfpy            : None
openpyxl         : 3.0.2
pandas_gbq       : None
pyarrow          : None
pytables         : None
pytest           : None
pyxlsb           : None
s3fs             : None
scipy            : 1.2.1
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : 1.2.0
xlwt             : None
xlsxwriter       : None
numba            : None
</details>
