License Mapping for BSD-3-Clause and BSD-4-Clause

With this addition to license mappings in PR #195
https://github.com/CycloneDX/cyclonedx-core-java/blob/b664a13f3e7c41a7e086ec508d804c2bd4207140/src/main/resources/license-mapping.json#L67

The consequence is that the component [antlr4](https://github.com/antlr/antlr4) now maps to `BSD-4-Clause` when the intention of the antlr project is the the license should be`BSD-3-Clause`.

See [LICENSE.txt](https://github.com/antlr/antlr4/blob/master/LICENSE.txt)

From antlr4 POM:

```


The BSD License
http://www.antlr.org/license.html
repo


```

So, is this a problem with `cyclonedx-core-java` license mapping, or is it a problem with `antlr4` POM?

The consequence of thinking that a `BSD-3-Clause` is actually `BSD-4-Clause` is that the latter:
* Adds an "advertising clause" that requires an acknowledgment of the original source in all advertising material.
* Was rescinded in 1999
* Is not OSI-approved.

src/main/resources/license-mapping.json にある PR #195 で追加されたエントリから始め、その BSD マッピングを antlr4 の LICENSE.txt および issue に記載された POM の詳細と比較します。マッピングまたは POM のどちらが誤っているかを解決し、antlr4 が意図された BSD ライセンスとして識別されることを確実にすれば完了です。

索引モデルが issue の本文から書いたものです。