[SPARK-23509][BUILD] Upgrade commons-net from 2.2 to 3.1

## What changes were proposed in this pull request?

This PR avoids version conflicts of `commons-net` by upgrading commons-net from 2.2 to 3.1. We are seeing the following message during the build using sbt.

```
[warn] Found version conflict(s) in library dependencies; some are suspected to be binary incompatible:
...
[warn] 	* commons-net:commons-net:3.1 is selected over 2.2
[warn] 	    +- org.apache.hadoop:hadoop-common:2.6.5              (depends on 3.1)
[warn] 	    +- org.apache.spark:spark-core_2.11:2.4.0-SNAPSHOT    (depends on 2.2)
[warn]
```

[Here](https://commons.apache.org/proper/commons-net/changes-report.html) is a release history.

[Here](https://commons.apache.org/proper/commons-net/migration.html) is a migration guide from 2.x to 3.0.

## How was this patch tested?

Existing tests

Author: Kazuaki Ishizaki <ishizaki@jp.ibm.com>

Closes #20672 from kiszk/SPARK-23509.

dev/deps/spark-deps-hadoop-2.6

@@ -48,7 +48,7 @@ commons-lang-2.6.jar
 commons-lang3-3.5.jar
 commons-logging-1.1.3.jar
 commons-math3-3.4.1.jar
-commons-net-2.2.jar
+commons-net-3.1.jar
 commons-pool-1.5.4.jar
 compress-lzf-1.0.3.jar
 core-1.1.2.jar

dev/deps/spark-deps-hadoop-2.7

@@ -48,7 +48,7 @@ commons-lang-2.6.jar
 commons-lang3-3.5.jar
 commons-logging-1.1.3.jar
 commons-math3-3.4.1.jar
-commons-net-2.2.jar
+commons-net-3.1.jar
 commons-pool-1.5.4.jar
 compress-lzf-1.0.3.jar
 core-1.1.2.jar

pom.xml

@@ -579,7 +579,7 @@
       <dependency>
         <groupId>commons-net</groupId>
         <artifactId>commons-net</artifactId>
-        <version>2.2</version>
+        <version>3.1</version>
       </dependency>
       <dependency>
         <groupId>io.netty</groupId>