Unhandled TypeError on non-alphanumeric keys

Non-alphanumeric keys, e.g. `,/?.`, cause a TypeError on keypress.

````
/home/eyko/github/node-term-list/index.js:57
  switch (key.name) {
             ^
TypeError: Cannot read property 'name' of undefined
    at List.onkeypress (/home/eyko/github/node-term-list/index.js:57:14)
    at ReadStream.EventEmitter.emit (events.js:98:17)
    at emitKey (/home/eyko/github/node-term-list/node_modules/keypress/index.js:406:12)
    at ReadStream.onData (/home/eyko/github/node-term-list/node_modules/keypress/index.js:48:14)
    at ReadStream.EventEmitter.emit (events.js:95:17)
    at ReadStream.<anonymous> (_stream_readable.js:746:14)
    at ReadStream.EventEmitter.emit (events.js:92:17)
    at emitReadable_ (_stream_readable.js:408:10)
    at emitReadable (_stream_readable.js:404:5)
    at readableAddChunk (_stream_readable.js:165:9)
````

@ledbettj reported it over here: turingou/btc#1 so stopping the event from being triggered would prevent the same error when requiring the lib.