Use the full flag notation

youtube_dl/downloader/external.py

@@ -183,7 +183,7 @@ class Aria2cFD(ExternalFD):
 
     def _make_cmd(self, tmpfilename, info_dict):
         cmd = [self.exe]
-        cmd += self._valueless_option('-c', 'continuedl')
+        cmd += self._bool_option('--continue', 'continuedl', separator='=')
         cmd += self._configuration_args([
             '--min-split-size', '1M', '--max-connection-per-server', '4'])
         dn = os.path.dirname(tmpfilename)