Static assets now allows setting custom headers & support for converting empty strings to null

• chore: downgrade strip-ansi as it works with ES modules only a617e3d
• chore: downgrade stringify-attributes as it works with ES modules only 2064b72
• refactor: remove import from contract file 8486ca7
• chore: update dependencies f6d3a98
• feat: add convertEmptyStringsToNull option to bodyparser config stub 1bdb45d
• feat: add static config to define custom headers d5ce5a7
• chore: update dependencies b4762f4
• style(typo): in repl bindings c3a29e8

v5.1.4...v5.1.5