Milestone warning is displayed when pluginpath is used

[suyograo]

--pluginpath can be used with LS to load plugins which are not converted into RubyGems yet. LS will output a warning when used with this option:

:message=>"abc plugin is using the 'milestone' method to declare the version of the plugin this method is deprecated in favor of declaring the version inside the gemspec.", :level=>:warn}

This is a benign message, and can be ignored, but we need to remove this warning so it does not confuse users.

[ph]

I came around this issue myself when working on metrics, I suggest we move the log level to debug?

[ph]

And we remove the support for milestone in the next major version.