Better error handling when parsing message

[ianshward]

If this JSON.parse is done in a try/catch it'd be possible to point out incorrectly formatted json when the parsing fails. We've seen at least one bad message come through:

SyntaxError: Unexpected token } in JSON at position 174
at Object.parse (native)
at /var/task/incoming/function.js:28:26
at /var/task/lib/utils.js:15:7
at /var/task/node_modules/decrypt-kms-env/index.js:21:5
at Queue._call (/var/task/node_modules/decrypt-kms-env/index.js:67:5)
at maybeNotify (/var/task/node_modules/d3-queue/build/d3-queue.js:120:7)
at /var/task/node_modules/d3-queue/build/d3-queue.js:91:12
at Response. (/var/task/node_modules/decrypt-kms-env/index.js:61:9)
at Request. (/var/task/node_modules/aws-sdk/lib/request.js:364:18)
at Request.callListeners (/var/task/node_modules/aws-sdk/lib/sequential_executor.js:105:20)
at Request.emit (/var/task/node_modules/aws-sdk/lib/sequential_executor.js:77:10)
at Request.emit (/var/task/node_modules/aws-sdk/lib/request.js:683:14)
at Request.transition (/var/task/node_modules/aws-sdk/lib/request.js:22:10)
at AcceptorStateMachine.runTo (/var/task/node_modules/aws-sdk/lib/state_machine.js:14:12)
at /var/task/node_modules/aws-sdk/lib/state_machine.js:26:10
at Request. (/var/task/node_modules/aws-sdk/lib/request.js:38:9)

cc @k-mahoney @alulsh

[alulsh]

I have a fix for this over in https://github.com/mapbox/dispatch/pull/106.

[k-mahoney]

#106 merged.