Note: this was causing a weird flake8 error on CI. Presumably due to CI running flake8 via py3.7.
```
flake8 . --count --select=$ELECTRUM_LINTERS --show-source --statistics
./electrum/scripts/update_default_servers.py:1:26: E999 SyntaxError: invalid syntax
#!/usr/bin/env python3
^
1 E999 SyntaxError: invalid syntax
1
```