[MINOR] Fix Typos 'a -> an'

## What changes were proposed in this pull request?

`a` -> `an`

I use regex to generate potential error lines:
`grep -in ' a [aeiou]' mllib/src/main/scala/org/apache/spark/ml/*/*scala`
and review them line by line.

## How was this patch tested?

local build
`lint-java` checking

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #13317 from zhengruifeng/a_an.

1 files changed, 1 insertions, 1 deletions

diff --git a/examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java b/examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java
index 1cba565b38..e20b94d5b0 100644
--- a/examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java
+++ b/examples/src/main/java/org/apache/spark/examples/streaming/JavaCustomReceiver.java
@@ -70,7 +70,7 @@ public class JavaCustomReceiver extends Receiver<String> {
     SparkConf sparkConf = new SparkConf().setAppName("JavaCustomReceiver");
     JavaStreamingContext ssc = new JavaStreamingContext(sparkConf, new Duration(1000));
 
-    // Create a input stream with the custom receiver on target ip:port and count the
+    // Create an input stream with the custom receiver on target ip:port and count the
     // words in input stream of \n delimited text (eg. generated by 'nc')
     JavaReceiverInputDStream<String> lines = ssc.receiverStream(
       new JavaCustomReceiver(args[0], Integer.parseInt(args[1])));