BUG: pandas dataframe style render produces incorrect html with multiindex
- [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.

---

**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
# Your code here
import pandas as pd
import datetime

df = pd.DataFrame(
    data={
        ('level0', 'level1a',): [1234565.23424],
        ('level0', 'level1b',): [1234565.23424],
        ('level0', 'level1c',): [1234565.23424],
        ('level0', 'level1d',): [1234565.23424],
        ('level0', 'level1e',): [1234565.23424],
    },
    columns=pd.MultiIndex.from_tuples(
        [
            ('level0', 'level1a',),
            ('level0', 'level1b',),
            ('level0', 'level1c',),
            ('level0', 'level1d',),
            ('level0', 'level1e',),
        ]
    ),
    index=['test']
)

df.style.format('{:,.2f}').render()
```

#### Problem description
The render() of the styler produces incorrect html in case the columns are a MultiIndex.

#### Expected Output
re.sub(r'colspan=(\d)', r'colspan="\1"', df.style.format('{:,.2f}').render())

The current implementation returns something like
<th class="col_heading level0 col0" colspan=5> while it should be
<th class="col_heading level0 col0" colspan="5">

See also https://www.w3schools.com/tags/att_td_colspan.asp

Same goes for MultiIndex indices where it concerns rowspan instead of colspan.

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

<details>

INSTALLED VERSIONS
------------------
commit           : d9fff2792bf16178d4e450fe7384244e50635733
python           : 3.6.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.14.111-1.el7.centos.x86_64
Version          : #1 SMP Wed Apr 17 17:45:41 CEST 2019
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.0
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 9.0.1
setuptools       : 28.8.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : 2.8.5 (dt dec pq3 ext lo64)
jinja2           : 2.11.2
IPython          : 7.14.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.0
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 1.0.0
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : None
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None

</details>
