Passsing assert_polygons a GeoDataFrame #175
Description
If a GeoDataFrame is passed into VectorTester.assert_polygons() as the polygons_expected, the test fails bc it is not a list of coordinates. There is a helper function called _convert_multipolygons that properly converts the GeoDataFrame into a list of coordinates. However, it is not called in the assert_polygons() function. There should be a check to see if the input is a GeoDataFrame and if it is the function _convert_multipolygons should be called within the function assert_polygons(). @lwasser