Javadoc.

- Remove Java 6 reference.
- Add Java 13 reference.

Author: garydgregory

src/main/java/org/apache/commons/codec/digest/MessageDigestAlgorithms.java

@@ -32,8 +32,6 @@
  * Java 9 and up: SHA3-224, SHA3-256, SHA3-384, SHA3-512.
  * </p>
  *
- * @see <a href="http://docs.oracle.com/javase/6/docs/technotes/guides/security/StandardNames.html#MessageDigest">
- *      Java 6 Cryptography Architecture Standard Algorithm Name Documentation</a>
  * @see <a href="http://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#MessageDigest">
  *      Java 7 Cryptography Architecture Standard Algorithm Name Documentation</a>
  * @see <a href="http://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html#MessageDigest">
@@ -46,6 +44,8 @@
  *      Java 11 Cryptography Architecture Standard Algorithm Name Documentation</a>
  * @see <a href="https://docs.oracle.com/en/java/javase/12/docs/specs/security/standard-names.html#messagedigest-algorithms">
  *      Java 12 Cryptography Architecture Standard Algorithm Name Documentation</a>
+ * @see <a href="https://docs.oracle.com/en/java/javase/13/docs/specs/security/standard-names.html#messagedigest-algorithms">
+ *      Java 13 Cryptography Architecture Standard Algorithm Name Documentation</a>
  *
  * @see <a href="http://dx.doi.org/10.6028/NIST.FIPS.180-4">FIPS PUB 180-4</a>
  * @see <a href="http://dx.doi.org/10.6028/NIST.FIPS.202">FIPS PUB 202</a>