Fixes help error on unknown command

TypeError: Uncaught, unspecified "error" event.
  at TypeError (<anonymous>:null:null)
  at Session.EventEmitter.emit (events.js:74:15)
  at Request._callback (/Users/abe/github/hubot/hubot-2.2.0/node_modules/hubot-flowdock/node_modules/flowdock/lib/flowdock.js:86:17)
  at Request.self.callback (/Users/abe/github/hubot/hubot-2.2.0/node_modules/hubot-flowdock/node_modules/flowdock/node_modules/request/main.js:122:22)
  at Request.EventEmitter.emit (events.js:98:17)
  at Request.<anonymous> (/Users/abe/github/hubot/hubot-2.2.0/node_modules/hubot-flowdock/node_modules/flowdock/node_modules/request/main.js:661:16)
  at Request.EventEmitter.emit (events.js:117:20)
  at IncomingMessage.<anonymous> (/Users/abe/github/hubot/hubot-2.2.0/node_modules/hubot-flowdock/node_modules/flowdock/node_modules/request/main.js:623:14)
  at IncomingMessage.EventEmitter.emit (events.js:117:20)
  at _stream_readable.js:870:14
  at process._tickCallback (node.js:415:13)