Add support for Maven Toolchain Plugin

The Maven compiler plugin now supports multiple JDK’s via their toolchain plugin, more information may be found here IMHO Toolchains would be an outstanding feature to add to TravisCI, in general.

Our project requires the plugin due to changes in our build process.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-toolchains-plugin:3.0.0:toolchain (default) on project red5-io: Cannot find matching toolchain definitions for the following toolchain types:
[ERROR] jdk [ version='[1.11,)' ]
[ERROR] Please make sure you define the required toolchains in your ~/.m2/toolchains.xml file.

Failing build: