[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.