Policies plugin version was not increased when integrated into core

The $plugin->version was not raised when tool_policy was integrated into core in MDL-62800. I think it should be increased so that

• the versions in the plugins directory will always and forever have lower version number that the ones in the standard distribution, and
• we have a reserve in the CONTRIB to still eventually increase the version number, should we need it.

I found this because I was thinking of adding a new version 2017111312 to the plugins directory that would display a warning if it finds itself running on the Moodle version released on 10 September.