obs-ffmpeg: Don't allow 32kb/s with FFmpeg AAC encoder

FFmpeg's AAC encoder is unideal at very low bitrates.

Closes jp9000/obs-studio#722

plugins/obs-ffmpeg/obs-ffmpeg-aac.c

@@ -259,7 +259,7 @@ static obs_properties_t *aac_properties(void *unused)
 	obs_properties_t *props = obs_properties_create();
 
 	obs_properties_add_int(props, "bitrate",
-			obs_module_text("Bitrate"), 32, 320, 32);
+			obs_module_text("Bitrate"), 64, 320, 32);
 	return props;
 }