[options] Prefer --convert-subs spelling

youtube_dl/options.py

@@ -752,7 +752,7 @@ def parseOpts(overrideArguments=None):
         metavar='CMD', dest='exec_cmd',
         help='Execute a command on the file after downloading, similar to find\'s -exec syntax. Example: --exec \'adb push {} /sdcard/Music/ && rm {}\'')
     postproc.add_option(
-        '--convert-subtitles', '--convert-subs',
+        '--convert-subs', '--convert-subtitles',
         metavar='FORMAT', dest='convertsubtitles', default=None,
         help='Convert the subtitles to other format (currently supported: srt|ass|vtt)')