Add <code> tag

Author: andrewor14

docs/configuration.md

@@ -562,15 +562,15 @@ Apart from these, the following properties are also available, and may be useful
   </td>
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 <tr>
-    <td>spark.hadoop.validateOutputSpecs</td>
+    <td><code>spark.hadoop.validateOutputSpecs</code></td>
     <td>true</td>
     <td>If set to true, validates the output specification (e.g. checking if the output directory already exists)
     used in saveAsHadoopFile and other variants. This can be disabled to silence exceptions due to pre-existing
     output directories. We recommend that users do not disable this except if trying to achieve compatibility with
     previous versions of Spark. Simply use Hadoop's FileSystem API to delete output directories by hand.</td>
 </tr>
 <tr>
-    <td>spark.executor.heartbeatInterval</td>
+    <td><code>spark.executor.heartbeatInterval</code></td>
     <td>10000</td>
     <td>Interval (milliseconds) between each executor's heartbeats to the driver.  Heartbeats let
     the driver know that the executor is still alive and update it with metrics for in-progress