Paradox 0.6.8

Changes

• Scaladoc: better support for inner classes #397 by @ennru
• Linking to javadoc inner classes #395 by @raboof
• Fix default javadoc base for jdk11+ #394 by @raboof
• Fail for regular links to .md #393 by @ennru

Updates

• Update sbt-header to 5.3.1 #391 by @scala-steward
• Update scalatest to 3.1.0 #392 by @scala-steward
• Update sbt-paradox to 0.6.7 #389 by @scala-steward
• Update sbt, scripted-plugin to 1.3.4 #390 by @scala-steward