Issue in Valhalla distances

[gmcrocetti]

Hello @nilsnolde ,

Great library, it helps me a lot.

I believe we have a problem in how distances of the Valhalla router are computed.

There are two places where this happens:

1. In the directions response:

   routingpy/routingpy/routers/valhalla.py

   Line 277 in a86cee6

   factor = 0.621371 if units == "mi" else 1

2. In matrix computation:

   routingpy/routingpy/routers/valhalla.py

   Line 653 in a86cee6

   factor = 0.621371 if units == "mi" else 1

So consider the following request:

valhalla_client = Valhalla()

points = [[-122.332070, 47.606210], [-122.200676, 47.610378]]  # Seattle, WA to Bellevue, WA ~10.4 miles
result = valhalla_client.matrix(points, profile="auto", sources=[0], destinations=[1], units="mi")

The response should be ~10.4 (using google maps as the source of truth) but it is 6416 which is ~10.4 * 0.621371 * 1000. Despite Valhalla responding in miles it is converted again.

I'm going to submit a patch for this, makes sense ?