chore: Add Serializable to FFmpegError

Author: Euklios

src/main/java/net/bramp/ffmpeg/FFmpegException.java

@@ -7,7 +7,7 @@
 public class FFmpegException extends IOException {
 
     private static final long serialVersionUID = 3048288225568984942L;
-    private FFmpegError error;
+    private final FFmpegError error;
 
     public FFmpegException(String message, FFmpegError error) {
         super(message);

src/main/java/net/bramp/ffmpeg/probe/FFmpegError.java

@@ -2,10 +2,14 @@
 
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 
+import java.io.Serializable;
+
 @SuppressFBWarnings(
     value = {"UUF_UNUSED_PUBLIC_OR_PROTECTED_FIELD"},
     justification = "POJO objects where the fields are populated by gson")
-public class FFmpegError {
+public class FFmpegError implements Serializable {
+  private static final long serialVersionUID = 1L;
+
   public int code;
   public String string;