The documentation for google_travel_time was at odds with the
implementation. The documentation stated a default scan time of
5 minutes, but the implementation was using Throttle which resulted
in the sensor updating at a maximum rate of one API call every
5 minutes. This was especially at odds with a given example at
the end of the documentation, which showed updating the sensor
every 2 minutes during commute times.
This change brings the implementation in line with the docs by
adopting the `SCAN_INTERVAL` constant set to the stated default
of 5 minutes and removing the Throttle.
2d3b117cb8