Update ddocs.rst (#533)

Improvement to "3.1.2.2. Reduce and Rereduce Functions" argument description #517

Co-authored-by: Sunitha Rajaretnam <srajaret@in.ibm.com>
diff --git a/src/ddocs/ddocs.rst b/src/ddocs/ddocs.rst
index 08290a1..a3e4efc 100644
--- a/src/ddocs/ddocs.rst
+++ b/src/ddocs/ddocs.rst
@@ -97,7 +97,7 @@
 
 .. function:: redfun(keys, values[, rereduce])
 
-    :param keys: Array of pairs of docid-key for related map function results.
+    :param keys: Array of pairs of key-docid for related map function results.
                  Always ``null`` if rereduce is running (has ``true`` value).
     :param values: Array of map function result values.
     :param rereduce: Boolean flag to indicate a rereduce run.