Fixes a bug with an invalid command for audio conversion

src/main/java/net/knarcraft/ffmpegconverter/converter/AudioConverter.java

@@ -35,6 +35,7 @@ public class AudioConverter extends AbstractConverter {
         //Gets the first audio stream from the file and adds it to the output file
         AudioStream audioStream = getFirstAudioSteam(streams);
         FFMpegHelper.addAudioStream(command, audioStream, false);
+        command.add(outFile);
 
         return command.toArray(new String[0]);
     }