[SPARK-11779][DOCS] Fix reference to deprecated MESOS_NATIVE_LIBRARY

MESOS_NATIVE_LIBRARY was renamed in favor of MESOS_NATIVE_JAVA_LIBRARY. This commit fixes the reference in the documentation.

Author: Philipp Hoffmann <mail@philipphoffmann.de>

Closes #9768 from philipphoffmann/patch-2.

docs/running-on-mesos.md

@@ -278,7 +278,7 @@ See the [configuration page](configuration.html) for information on Spark config
     Set the name of the docker image that the Spark executors will run in. The selected
     image must have Spark installed, as well as a compatible version of the Mesos library.
     The installed path of Spark in the image can be specified with <code>spark.mesos.executor.home</code>;
-    the installed path of the Mesos library can be specified with <code>spark.executorEnv.MESOS_NATIVE_LIBRARY</code>.
+    the installed path of the Mesos library can be specified with <code>spark.executorEnv.MESOS_NATIVE_JAVA_LIBRARY</code>.
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