Allow attraction=big_wheel to be mapped as an area (#989)

As per wiki https://wiki.openstreetmap.org/wiki/Tag:attraction%3Dbig_wheel,
this feature can also be mapped as an area and it is already used as such.
So this fixes the validation to allow definiting is an area and remove
warnings.

Author: andreadecorte

data/presets/attraction/big_wheel.json

@@ -10,7 +10,8 @@
         "min_age"
     ],
     "geometry": [
-        "point"
+        "point",
+        "area"
     ],
     "terms": [
         "ferris wheel",