I got the following warning from Little Snitch on OS X 11.12. It occurred after launching the SmartenPunctuation plugin.
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Sigil via Python
wants to connect to gist.githubusercontent.com on TCP port 443 (https)
IP Address 151.101.24.133
Reverse DNS Name No Reverse Name
Established by /private/var/folders/07/g6vclvb95_n_xk57230_rplw0000gn/T/AppTranslocation/EA409584-1824-47AC-BDEC-0ED1454834A0/d/Sigil.app/Contents/Frameworks/Python.framework/Versions/3.5/Resources/Python.app/Contents/MacOS/Python
Process ID 23459
User _______ (UID: 501)
Parent Application /private/var/folders/07/g6vclvb95_n_xk57230_rplw0000gn/T/AppTranslocation/EA409584-1824-47AC-BDEC-0ED1454834A0/d/Sigil.app/Contents/MacOS/Sigil
Process ID 15643
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http://151.101.24.133/ is a GitHub page site. Should Sigil try connecting remotely when launching a plugin?