BUG: pd.show_versions: json.decoder.JSONDecodeError
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

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**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
import contextlib, io, json
import pandas as pd

redirect = io.StringIO()
with contextlib.redirect_stdout(redirect):
    pd.show_versions(as_json=True)  # produces invalid json
pd_versions = redirect.getvalue()
pd_versions = json.loads(pd_versions)  # raises JSONDecodeError
```

#### Problem description

`pd.show_versions(as_json=True)` is supposed to print valid JSON, but it really doesn't. It is supposed to work as advertised but it doesn't. It prints invalid JSON that is not parsable. The following error is printed when attempting to parse it:

> json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 1 column 2 (char 1)

This functionality is important because when running a job in the cloud, it is not feasible to print a multiline output. This is because every printed line has significant attached metadata. It is better to have valid JSON output instead in this case. The implementation of the `show_versions` function looks to be very hacky and poorly reviewed, given that it fails in this very basic way.

#### Expected Output

In the code example, `json.loads(pd_versions)` should have been able to parse the captured text.

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

<details>

INSTALLED VERSIONS
------------------
commit           : 7d32926db8f7541c356066dcadabf854487738de
python           : 3.8.6.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 19.6.0
Version          : Darwin Kernel Version 19.6.0: Tue Nov 10 00:10:30 PST 2020; root:xnu-6153.141.10~1/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : en_US.UTF-8
pandas           : 1.2.2
numpy            : 1.19.4
pytz             : 2020.4
dateutil         : 2.8.1
pip              : 21.0.1
setuptools       : 50.3.2
Cython           : None
pytest           : 6.2.2
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 3.0.0
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
