Update site.MESOS_VERSIOn to match /pom.xml

Author: ash211

docs/_config.yml

@@ -7,6 +7,6 @@ SPARK_VERSION: 1.0.0-SNAPSHOT
 SPARK_VERSION_SHORT: 1.0.0
 SCALA_BINARY_VERSION: "2.10"
 SCALA_VERSION: "2.10.4"
-MESOS_VERSION: 0.13.0
+MESOS_VERSION: 0.18.1
 SPARK_ISSUE_TRACKER_URL: https://issues.apache.org/jira/browse/SPARK
 SPARK_GITHUB_URL: https://github.com/apache/spark