Fixed Google Maps url in the event detail

Gijs Hendriksen
2018-11-08T17:16:52+01:00

Closes #80

#### Previous behaviour
The Google Maps image at the top of the detail screen would not render.

Steps to reproduce:

1. Open an event (preferably one with a unique location you haven't seen yet, as React Native caches images).
2. Notice the map at the top does not render.

#### New behaviour
The Google Maps image at the top of the detail screen renders normally.

Steps to validate that it works:

1. Open an event (preferably one with a unique location you haven't seen yet, as React Native caches images).
2. Notice the map at the top renders fine.