``_get_proxy_list()`` not updated to new API

[oesteban]

Describe the bug
A clear and concise description of what the bug is.

This line crashes with the new API:

scholarly/scholarly/_proxy_generator.py

Line 518 in 9269ff3

all_proxies = freeproxy.get_proxy_list()

To Reproduce
I'm guessing that this can be reproduced when no proxies are identified immediately above:
github.com/scholarly-python-package/scholarly/blob/9269ff36ad2314e6cc0c5b499efc3b79b844707e/scholarly/_proxy_generator.py#L508-L511

(please note how the call is protected with a try catch there)

Expected behavior
Should not crash

Do you plan on contributing?
Your response below will clarify whether the maintainers can expect you to fix the bug you reported.

• Yes, I will create a Pull Request with the bugfix.

Additional context
Add any other context about the problem here.