refactor: add serialVersionUID field to exception classes

src/main/java/de/stklcode/jvault/connector/exception/AuthorizationRequiredException.java

@@ -23,4 +23,5 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public class AuthorizationRequiredException extends VaultConnectorException {
+    private static final long serialVersionUID = 2629577936657393880L;
 }

src/main/java/de/stklcode/jvault/connector/exception/ConnectionException.java

@@ -23,6 +23,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public class ConnectionException extends VaultConnectorException {
+    private static final long serialVersionUID = 3005430116002990418L;
+
     /**
      * Constructs a new empty exception.
      */

src/main/java/de/stklcode/jvault/connector/exception/InvalidRequestException.java

@@ -23,6 +23,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public class InvalidRequestException extends VaultConnectorException {
+    private static final long serialVersionUID = -6712239648281809159L;
+
     /**
      * Constructs a new empty exception.
      */

src/main/java/de/stklcode/jvault/connector/exception/InvalidResponseException.java

@@ -24,6 +24,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public final class InvalidResponseException extends VaultConnectorException {
+    private static final long serialVersionUID = 2003151038614163479L;
+
     private final Integer statusCode;
     private final String response;
 

src/main/java/de/stklcode/jvault/connector/exception/PermissionDeniedException.java

@@ -23,6 +23,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public class PermissionDeniedException extends VaultConnectorException {
+    private static final long serialVersionUID = -7149134015090750776L;
+
     /**
      * Constructs a new empty exception.
      */

src/main/java/de/stklcode/jvault/connector/exception/TlsException.java

@@ -23,6 +23,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.4.0
  */
 public class TlsException extends VaultConnectorException {
+    private static final long serialVersionUID = -5139276834988258086L;
+
     /**
      * Constructs a new empty exception.
      */

src/main/java/de/stklcode/jvault/connector/exception/VaultConnectorException.java

@@ -23,6 +23,8 @@ package de.stklcode.jvault.connector.exception;
  * @since 0.1
  */
 public abstract class VaultConnectorException extends Exception {
+    private static final long serialVersionUID = -2612477894310906036L;
+
     /**
      * Constructs a new empty exception.
      */