doclet in maven-javadoc-plugin with JDK10 - complains invalid tag "-author"?

Hi,

I'm seeing the following when building with Maven 3.5.4 and maven-javadoc-plugin 3.0.1 with Maven using Java 10.0.1 (on Linux Mint, dot - graphviz version 2.38.0 (20140413.2041)).

```
org.apache.maven.reporting.MavenReportException:
Exit code: 1 - javadoc: warning - The old Doclet and Taglet APIs in the packages
com.sun.javadoc, com.sun.tools.doclets and their implementations
are planned to be removed in a future JDK release. These
components have been superseded by the new APIs in jdk.javadoc.doclet.
Users are strongly recommended to migrate to the new APIs.
javadoc: error - invalid flag: -author

```
If I comment out the doclet then the build succeeds, so while I've github-searched this repo for 'author' and can find no relevant reference, the issue appears somewhere in here.

It's not a show-stopper for Maven users - if they use toolchains for their own code and set the Java version Maven uses to <= 1.9 then all's good. But JDK's have a limited shelf life these days.

Error message above is a strong indication of Oracle aggressive approach to advancing the platform while still purporting backwards compatibility - stuff that's been relied on for a decade or more, deprecated and then broken/borken rather too quickly.

In all seriousness, this doclet running in a Maven build, is the _only reason_ I bother to generate JavaDoc. It's UML loveliness is widely spread (e.g. https://www.javadoc.io/doc/io.earcam.wrapped/com.sun.tools.attach/1.8.0_jdk8u172-b11 or even better https://static.javadoc.io/io.earcam.wrapped/jdk.compiler/1.8.132/com/sun/tools/javac/tree/package-summary.html large monitor required 😀)

Side note; regarding issue #46 - things have got _a lot_ easier WRT Maven releases, I'd be more than happy to help resolve that issue and this.

Thank you 👍