Fix link in connect docstring (MagicStack#653)

Author: samuelcolvin

asyncpg/connection.py

@@ -1919,7 +1919,7 @@ async def connect(dsn=None, *,
  .. _postgres envvars:
  https://www.postgresql.org/docs/current/static/libpq-envars.html
  .. _libpq connection URI format:
- https://www.postgresql.org/docs/current/static/\
+ https://www.postgresql.org/docs/current/static/
  libpq-connect.html#LIBPQ-CONNSTRING
  """
  if not issubclass(connection_class, Connection):