I have `rethinkdb==2.3.0.post6` and `Python 3.7.2`. When I set `r.set_loop_type('asyncio')`, I get an error: ``` File ".../rethinkdb/asyncio_net/net_asyncio.py", line 114 asyncio.async(self.conn._parent._continue(self)) ^ SyntaxError: invalid syntax ``` Fix this, please.