inkscape: Handle changes in Inkscape 1.0

Inkscape 1.0 final has replaced the '--export-file' argument with
'--export-filename' [1]. Update our calls accordingly.

[1] https://wiki.inkscape.org/wiki/index.php/Release_notes/1.0#Command_Line

Signed-off-by: Stephen Finucane <stephen@that.guru>
Closes: rst2pdf#869

rst2pdf/extensions/inkscape_r2p.py

@@ -69,11 +69,12 @@ def __init__(
                 # Inkscape 0.x uses -A
                 cmd = [progname, os.path.abspath(filename), '-A', pdffname]
             else:
-                # Inkscape 1.x uses --export-file
+                # Inkscape 1.x uses --export-filename
                 cmd = [
                     progname,
                     os.path.abspath(filename),
-                    '--export-file=%s' % pdffname,
+                    '--export-filename',
+                    pdffname,
                 ]
             try:
                 result = subprocess.call(cmd)
@@ -119,11 +120,12 @@ def raster(self, filename, client):
                     str(client.def_dpi),
                 ]
             else:
-                # Inkscape 1.x uses --export-file
+                # Inkscape 1.x uses --export-filename
                 cmd = [
                     progname,
                     os.path.abspath(filename),
-                    '--export-file=%s' % pngfname,
+                    '--export-filename',
+                    pngfname,
                     '-d',
                     str(client.def_dpi),
                 ]