refactor to support only 2.10.6+, 2.11.8+ and 2.12.x

[kailuowang]

Thanks for your nice work. I'd like to recommend this plugin to typelevel/cats users once we get rid of the Unapply machinery per this issue

I made some changes here

1. support 2.11.9+ with the scalacOption
2. stop supporting versions prior to 2.10.6 and after 2.13, for 2.10.6- there is no plugin available. For 2.14+ it's too far ahead we don't know if the flag is still supported, by that time this plugin is probably obsolete.
3. Fail when the scala version falls out of the supported range which is 2.10.6 - 2.13.x

[fiadliel]

Sorry, this was marked as "not watched", so I didn't see this. Changes look good to me.

Separately, I need to make sure it does the right thing if scalaOrganization is set for TLS, but that can be a different change.

[kailuowang]

no worries. Do you plan to release this change or after the scalaOrganization change?

[fiadliel]

The scalaOrganization check is just a small correction, it can be done in a patch update. Released 1.0.0.

[kailuowang]

Thanks