fix gdal import statement
old style imports (ie import gdal
instead of from osgeo import gdal
) are no longer available since gdal 3.2
ref : https://github.com/OSGeo/gdal/commit/669c491923ed0473b63e2baee7b7a33f3018761f
old style imports (ie import gdal
instead of from osgeo import gdal
) are no longer available since gdal 3.2
ref : https://github.com/OSGeo/gdal/commit/669c491923ed0473b63e2baee7b7a33f3018761f