v0.5.6

Changelog

• 2fc62a6: Merge pull request #51 from jonhadfield/readme-proxy-env (@jonhadfield)
• 4e3dd94: Merge pull request #52 from jonhadfield/fix/cask-postflight-deprecation (@jonhadfield)
• cffc697: README: document proxy environment variable support (@jonhadfield)
• 274bc88: Stop the cask emitting Homebrew's deprecated postflight (@jonhadfield)