Don't log headers

[zachmargolis]

Why:

1. They were being serialized incorrectly
2. They could potentially contain sensitive data

---

before (note the "headers":"#<ActionDispatch::Http::Headers:0x007ff1b05abcd0>")

{"method":"GET","path":"/api/health/workers.json","format":"json","controller":"Health::WorkersController","action":"index","status":200,"duration":504.3,"headers":"#<ActionDispatch::Http::Headers:0x007ff1b05abcd0>","user_id":"anonymous-uuid","user_agent":"curl/7.54.0","ip":"::1","host":"localhost","timestamp":"2017-08-31 14:43:36 -0400","uuid":"c8f71f70-815f-4d42-bed1-44b18104c9f0"}

after

{"method":"GET","path":"/api/health/workers.json","format":"json","controller":"Health::WorkersController","action":"index","status":200,"duration":519.54,"user_id":"anonymous-uuid","user_agent":"curl/7.54.0","ip":"::1","host":"localhost","timestamp":"2017-08-31 14:44:27 -0400","uuid":"9b59e2a8-1ec9-464c-b186-49ce4df7b998"}

[monfresh]

LGTM