HADOOP-15705. Typo in the definition of "stable" in the interface classification

Change-Id: I3eae2143400a534903db4f186400561fc8d2bd56
(cherry picked from commit d53a10b0a552155de700e396fd7f450a4c5f9c22)
(cherry picked from commit 90c8cca78389f534429ebf81576ce7ebba9356f7)

hadoop-common-project/hadoop-common/src/site/markdown/InterfaceClassification.md

@@ -124,7 +124,7 @@ hence serves as a safe development target. A Stable interface may evolve
 compatibly between minor releases.
 
 Incompatible changes allowed: major (X.0.0)
-Compatible changes allowed: maintenance (x.Y.0)
+Compatible changes allowed: maintenance (x.y.Z)
 
 #### Evolving