Fix AttributeError exception

[petriborg]

• asyncpg version: 0.20.1
• PostgreSQL version: BDR 11.X
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?: No SaaS, local BDR
• Python version: 3.5.7
• Platform: RH Linux
• Do you use pgbouncer?: Yes
• Did you install asyncpg with pip?: Yes - but custom built
• If you built asyncpg locally, which version of Cython did you use?: 0.29.14
• Can the issue be reproduced under both asyncio and
  uvloop?: Unknown

Executing the following code results in AttributeError exception - 'object' has no attribute '__getattr__'

conn = await asyncpg.connect(dsn=...)
settings = conn.get_settings()
print(settings._settings)

I believe the function should be calling __getattribute__ instead - as in:

    def __getattr__(self, name):
        if not name.startswith('_'):
            try:
                return self._settings[name]
            except KeyError:
                raise AttributeError(name) from None

        return object.__getattribute__(self, name)

[elprans]

Thanks!