Fix case of 'Spark' in option description

Author: EnricoMi

core/src/main/scala/org/apache/spark/internal/config/UI.scala

@@ -221,7 +221,7 @@ private[spark] object UI {
     .createOptional
 
   val CUSTOM_DRIVER_LOG_URL = ConfigBuilder("spark.ui.custom.driver.log.url")
-    .doc("Specifies custom spark driver log url for supporting external log service instead of " +
+    .doc("Specifies custom Spark driver log url for supporting external log service instead of " +
       "using cluster managers' application log urls in the Spark UI. Spark will support " +
       "some path variables via patterns which can vary on cluster manager. Please check the " +
       "documentation for your cluster manager to see which patterns are supported, if any. " +
@@ -233,7 +233,7 @@ private[spark] object UI {
     .createOptional
 
   val CUSTOM_EXECUTOR_LOG_URL = ConfigBuilder("spark.ui.custom.executor.log.url")
-    .doc("Specifies custom spark executor log url for supporting external log service instead of " +
+    .doc("Specifies custom Spark executor log url for supporting external log service instead of " +
       "using cluster managers' application log urls in the Spark UI. Spark will support " +
       "some path variables via patterns which can vary on cluster manager. Please check the " +
       "documentation for your cluster manager to see which patterns are supported, if any. " +

docs/configuration.md

@@ -1627,7 +1627,7 @@ Apart from these, the following properties are also available, and may be useful
   <td><code>spark.ui.custom.driver.log.url</code></td>
   <td>(none)</td>
   <td>
-    Specifies custom spark driver log URL for supporting external log service instead of using cluster
+    Specifies custom Spark driver log URL for supporting external log service instead of using cluster
     managers' application log URLs in Spark UI. Spark will support some path variables via patterns
     which can vary on cluster manager. Please check the documentation for your cluster manager to
     see which patterns are supported, if any. <p/>
@@ -1641,7 +1641,7 @@ Apart from these, the following properties are also available, and may be useful
   <td><code>spark.ui.custom.executor.log.url</code></td>
   <td>(none)</td>
   <td>
-    Specifies custom spark executor log URL for supporting external log service instead of using cluster
+    Specifies custom Spark executor log URL for supporting external log service instead of using cluster
     managers' application log URLs in Spark UI. Spark will support some path variables via patterns
     which can vary on cluster manager. Please check the documentation for your cluster manager to
     see which patterns are supported, if any. <p/>