Fixed typo in help text (trivial).

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@9228 71c3de6d-444a-0410-be80-ed276b4c234a

war/resources/help/matrix/jdk.html

@@ -7,6 +7,6 @@
   Selecting multiple values is typically useful when this job is running tests,
   and you need to run tests on multiple different versions of JDKs.
   <br>
-  During a build, the selected JDK value for the given run is available as the "jdK" axis.
+  During a build, the selected JDK value for the given run is available as the "jdk" axis.
   See the help of "axes" below for more information about how to access the axis value.
 </div>
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