small errors in ConcurrentHashMap and LongAdder docs

The class doc for j.u.c.atomic.LongAdder has an incorrect example. The call to computeIfAbsent has the wrong number of arguments.

Suggested patch:

diff -r 79a6703ab839 src/share/classes/java/util/concurrent/atomic/LongAdder.java
--- a/src/share/classes/java/util/concurrent/atomic/LongAdder.java Thu May 29 15:50:36 2014 +0100
+++ b/src/share/classes/java/util/concurrent/atomic/LongAdder.java Fri May 30 16:11:03 2014 -0700
@@ -57,7 +57,7 @@
  * frequency map (a form of histogram or multiset). For example, to
  * add a count to a {@code ConcurrentHashMap<String,LongAdder> freqs},
  * initializing if not already present, you can use {@code
- * freqs.computeIfAbsent(k -> new LongAdder()).increment();}
+ * freqs.computeIfAbsent(key, k -> new LongAdder()).increment();}
  *
  * <p>This class extends {@link Number}, but does <em>not</em> define
  * methods such as {@code equals}, {@code hashCode} and {@code