Update javadoc links

Author: damianmalczewski

problem4j-jackson2/src/main/java/io/github/problem4j/jackson2/ProblemMixIn.java

@@ -32,7 +32,9 @@
 
 /**
  * Jackson MixIn that redirects serialization and deserialization of {@code Problem} through the
- * {@link ProblemBridge} POJO.
+ * internal {@link ProblemBridge} POJO.
+ *
+ * @see io.github.problem4j.core.Problem
  */
 @JacksonXmlRootElement(localName = PROBLEM, namespace = NAMESPACE)
 @JsonRootName(value = PROBLEM, namespace = NAMESPACE)

problem4j-jackson3/src/main/java/io/github/problem4j/jackson3/ProblemJacksonMixIn.java

@@ -31,7 +31,9 @@
 
 /**
  * Jackson MixIn that redirects serialization and deserialization of {@code Problem} through the
- * {@link ProblemBridge} POJO.
+ * internal {@link ProblemBridge} POJO.
+ *
+ * @see io.github.problem4j.core.Problem
  */
 @JsonRootName(value = PROBLEM, namespace = NAMESPACE)
 @JsonSerialize(converter = ConverterProblemToBridge.class)