Update spatial.rb (#16)

Hitting an issue like rgeo/rgeo-geojson#33 where we are getting "LinearRing failed ring test (RGeo::Error::InvalidGeometry)" for a valid polygon.  Added rescue from RGeo::Error::InvalidGeometry

lib/active_record/type/spatial.rb

@@ -91,7 +91,7 @@ def parse_wkt(string)
         else
           RGeo::WKRep::WKTParser.new(spatial_factory, support_ewkt: true, default_srid: @srid).parse(string)
         end
-      rescue RGeo::Error::ParseError
+      rescue RGeo::Error::ParseError, RGeo::Error::InvalidGeometry
         nil
       end
     end