Polish ClassPath

[nosan]

Introduced toString to fix the following:

	private void addClasspath(List<String> args) throws MojoExecutionException {
		try {
			ClassPath classpath = ClassPath.of(getClassPathUrls());
			if (getLog().isDebugEnabled()) {
				getLog().debug("Classpath for forked process: " + classpath);
			}
			args.addAll(classpath.args(true));
		}
		catch (Exception ex) {
			throw new MojoExecutionException("Could not build classpath", ex);
		}
	}

[philwebb]

Gahhhh! I knew I was going to forget to add a toString() when I was refactoring! Thanks for catching that @nosan!