Replace get_event_loop() with get_running_loop() for asyncio compatibility

[thombashi]

Hello,

I got DeprecationWarning: There is no current event loop when using dominate v2.9.1 with Python 3.10 or newer.
ref: thombashi/pytablewriter#66

According to the official Python 3.10 document:

In Python versions 3.10.0–3.10.8 and 3.11.0 this function (and other functions which use it implicitly) emitted a DeprecationWarning if there was no running event loop, even if the current loop was set on the policy. In Python versions 3.10.9, 3.11.1 and 3.12 they emit a DeprecationWarning if there is no running event loop and no current loop is set. In some future Python release this will become an error.

And it was deprecated in Python 3.12:

Deprecated since version 3.12: Deprecation warning is emitted if there is no current event loop. In some future Python release this will become an error.

The document suggests using the get_running_loop() function instead of get_event_loop() function.

This will resolve: #198

[coveralls]

coverage: 100.0%. remained the same
when pulling b4f4713 on thombashi:replace_get_event_loop
into 82dd9e7 on Knio:master.