Correct RFC 4648 references in method-level javadoc

Issue: SPR-14067

spring-core/src/main/java/org/springframework/util/Base64Utils.java

 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -99,7 +99,7 @@ public abstract class Base64Utils {
 	}
 
 	/**
-	 * Base64-encode the given byte array using the RFC 4868
+	 * Base64-encode the given byte array using the RFC 4648
 	 * "URL and Filename Safe Alphabet".
 	 * @param src the original byte array (may be {@code null})
 	 * @return the encoded byte array (or {@code null} if the input was {@code null})
@@ -113,7 +113,7 @@ public abstract class Base64Utils {
 	}
 
 	/**
-	 * Base64-decode the given byte array using the RFC 4868
+	 * Base64-decode the given byte array using the RFC 4648
 	 * "URL and Filename Safe Alphabet".
 	 * @param src the encoded byte array (may be {@code null})
 	 * @return the original byte array (or {@code null} if the input was {@code null})
@@ -174,7 +174,7 @@ public abstract class Base64Utils {
 	}
 
 	/**
-	 * Base64-encode the given byte array to a String using the RFC 4868
+	 * Base64-encode the given byte array to a String using the RFC 4648
 	 * "URL and Filename Safe Alphabet".
 	 * @param src the original byte array (may be {@code null})
 	 * @return the encoded byte array as a UTF-8 String
@@ -188,7 +188,7 @@ public abstract class Base64Utils {
 	}
 
 	/**
-	 * Base64-decode the given byte array from an UTF-8 String using the RFC 4868
+	 * Base64-decode the given byte array from an UTF-8 String using the RFC 4648
 	 * "URL and Filename Safe Alphabet".
 	 * @param src the encoded UTF-8 String (may be {@code null})
 	 * @return the original byte array (or {@code null} if the input was {@code null})