[sponskrub] Pass proxy to sponskrub

Needs atleast sponskrub version:
    faissaloo/sponskrub 3.7.0
    OR yt-dlp/sponskrub 2021.03.15

yt_dlp/postprocessor/sponskrub.py

@@ -6,6 +6,7 @@ from .common import PostProcessor
 from ..compat import compat_shlex_split
 from ..utils import (
     check_executable,
+    cli_option,
     encodeArgument,
     encodeFilename,
     shell_quote,
@@ -70,6 +71,7 @@ class SponSkrubPP(PostProcessor):
         cmd = [self.path]
         if not self.cutout:
             cmd += ['-chapter']
+        cmd += cli_option(self._downloader.params, '-proxy', 'proxy')
         cmd += compat_shlex_split(self.args)  # For backward compatibility
         cmd += self._configuration_args(self._exe_name, use_compat=False)
         cmd += ['--', information['id'], filename, temp_filename]