Fixed readme example

$ node index.js

/Users/kevireilly/Development/mail-listener2/index.js:15
  attachments: true, // download attachments as they are encountered to the pr
  ^^^^^^^^^^^
SyntaxError: Unexpected identifier
    at Module._compile (module.js:439:25)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:906:3