[SPARK-6350][Mesos] Make mesosExecutorCores configurable in mesos "fi…

…ne-grained" mode

- Fixed docs

docs/running-on-mesos.md

@@ -214,7 +214,7 @@ See the [configuration page](configuration.html) for information on Spark config
   <td><code>spark.mesos.executor.cores</code></td>
   <td>1.0</td>
   <td>
-    Set the amount of cores, which can be a floating point number, to request for running a mesos executor.
+    Set the amount of cores, which can be a floating point number, to request for running a Mesos executor.
     The setting controls the number of cores allocated to the executor not for use by tasks. By default,
     executor will use the amount of cores even though no task is running on an executor. This setting is
     only used for Mesos fine-grained mode.