Release v3.1.0

What's Changed

• latest chen by @prabhu in #254
• Expose frontend config via first-class flags and config file by @prabhu in #255
• json config only by @prabhu in #256
• [jssrc2cpg] babel 8 support with chen 3.1.0 by @prabhu in #257

Full Changelog: v3.0.3...v3.1.0