Fixed pyresample exception.

Signed-off-by: Daniel Scheffler <danschef@gfz-potsdam.de>

sensormapgeo/transformer_2d.py

@@ -321,7 +321,7 @@ class SensorMapGeometryTransformer(object):
                                                                                    float, float, float], str):
         gt = area_definition.area_extent[0], area_definition.pixel_size_x, 0, \
              area_definition.area_extent[3], 0, -area_definition.pixel_size_y
-        prj = area_definition.crs_wkt
+        prj = area_definition.crs.to_wkt()
 
         return gt, prj