Fix unclosed HTML tag in Yarn docs.

Author: JoshRosen

docs/running-on-yarn.md

@@ -75,7 +75,7 @@ Most of the configs are the same for Spark on YARN as for other deployment modes
   <td>(none)</td>
   <td>
     Comma-separated list of files to be placed in the working directory of each executor.
-  <td>
+  </td>
 </tr>
 <tr>
  <td><code>spark.yarn.executor.memoryOverhead</code></td>