[#23] Update to Maven 3.

[bmarwell]

Fixes #23

Did not check for unused dependencies.
PTAL at the warnings:

[WARNING] javadoc: warning - The code being documented uses modules but the packages defined in https://docs.oracle.com/javase/8/docs/api/ are in the unnamed module.

[WARNING] [APT Parser] Ambiguous link: 'usage.html'. If this is a local link, prepend "./"!
[WARNING] Could not parse date '24 March 2007' from index.apt (expected yyyy-MM-dd format), ignoring!
[WARNING] [APT Parser] Ambiguous link: 'taglist-mojo.html'. If this is a local link, prepend "./"!

[INFO] --- maven-plugin-plugin:3.6.0:descriptor (default) @ taglist-maven-plugin ---
[INFO] Using 'UTF-8' encoding to read mojo source files.
[WARNING] org.codehaus.mojo.taglist.TagListReport#aggregate:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] org.codehaus.mojo.taglist.TagListReport#encoding:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] org.codehaus.mojo.taglist.TagListReport#linkXRef:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] org.codehaus.mojo.taglist.TagListReport#project:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.
[WARNING] org.codehaus.mojo.taglist.TagListReport#reactorProjects:
[WARNING]   The syntax
[WARNING]     @parameter expression="${property}"
[WARNING]   is deprecated, please use
[WARNING]     @parameter property="property"
[WARNING]   instead.