Release 0.6.3 of the SPDX Maven Plugin

What's Changed

• Include transitive dependencies in SBOM output by @goneall in #63
• Implement options for creating external document refs and transitive dependencies by @goneall in #64
• Fix relationship direction and type for optional scope and for test scope by @goneall in #66
• Update SPDX library versions by @goneall in #67 - See the SPDX Java Library release notes for details

Full Changelog: v0.6.2...v0.6.3