CI: ResourceWarning in `pandas/tests/io/test_html.py`
It occurs occasionally on the travis-37-cov build.

```
_____________ TestReadHtml.test_banklist_url_positional_match[bs4] _____________

[gw0] linux -- Python 3.7.8 /home/travis/miniconda3/envs/pandas-dev/bin/python

self = <pandas.tests.io.test_html.TestReadHtml object at 0x7f40f8fef450>

    @tm.network

    def test_banklist_url_positional_match(self):

        url = "http://www.fdic.gov/bank/individual/failed/banklist.html"

        # Passing match argument as positional should cause a FutureWarning.

        with tm.assert_produces_warning(FutureWarning):

            df1 = self.read_html(

>               url, "First Federal Bank of Florida", attrs={"id": "table"}

            )

pandas/tests/io/test_html.py:130: 

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <contextlib._GeneratorContextManager object at 0x7f40f9070190>

type = None, value = None, traceback = None

    def __exit__(self, type, value, traceback):

        if type is None:

            try:

>               next(self.gen)

E               AssertionError: Caused unexpected warning(s): [('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=18, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 54722), raddr=('172.217.204.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=17, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 54720), raddr=('172.217.204.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=21, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 52284), raddr=('142.250.97.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=23, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 54628), raddr=('173.194.210.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=22, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 37618), raddr=('173.194.215.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=24, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 38812), raddr=('173.194.217.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=28, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 38824), raddr=('173.194.217.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85), ('ResourceWarning', ResourceWarning("unclosed <ssl.SSLSocket fd=27, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=6, laddr=('10.20.0.43', 54640), raddr=('173.194.210.95', 443)>"), '/home/travis/miniconda3/envs/pandas-dev/lib/python3.7/site-packages/html5lib/_utils.py', 85)]

../../../miniconda3/envs/pandas-dev/lib/python3.7/contextlib.py:119: AssertionError
```

