fix: require bash script plugin when packaging

[pvlugter]

Fixes #28. Make sure bash script plugin default settings are applied first.

[pvlugter]

A little trickier. This plugin still cross builds against sbt 0.13, and so it tests against much older versions of sbt-native-packager, which don't have BashStartScriptPlugin. And the sbt-native-packager 1.1.6 jar does contain a broken BashStartScriptPlugin class for some reason, even though it shouldn't be there based on the sources.

Could work around these, but wonder if it's time to move on from sbt 0.13 for this plugin? Older versions of the plugin can still be used.

[pvlugter]

As there's a broken BashStartScriptPlugin included in sbt-native-packager 1.1.6 for some reason, failing to load with:

java.lang.NoSuchMethodError: com.typesafe.sbt.packager.Keys$.bashScriptReplacements()Lsbt/TaskKey;

rather than making this plugin optional, have only included it for sbt 1.

[eed3si9n]

Thanks!