Fix issue with servoWrite & pwmWrite

I was hitting this error when trying to control my servo:

```
Servo on pin A0 turning counter clockwise

/Users/skalnik/github/catbot/node_modules/cylon-spark/dist/spark.js:94
        return analogWrite(pin, value);
               ^
ReferenceError: analogWrite is not defined
  at Spark.Spark.servoWrite (/Users/skalnik/github/catbot/node_modules/cylon-spark/dist/spark.js:94:16)
  at Connection.base.(anonymous function) [as servoWrite] (/Users/skalnik/github/catbot/node_modules/cylon-gpio/node_modules/cylon/dist/utils.js:33:31)
  at Servo.Servo.counterClockwise (/Users/skalnik/github/catbot/node_modules/cylon-gpio/dist/servo.js:71:34)
  at Device.base.(anonymous function) [as counterClockwise] (/Users/skalnik/github/catbot/node_modules/cylon-gpio/node_modules/cylon/dist/utils.js:33:31)
  at [object Object].<anonymous> (/Users/skalnik/github/catbot/catbot-cylon.coffee:16:9, <js>:25:26)
  at [object Object].wrapper [as _onTimeout] (timers.js:252:14)
  at Timer.listOnTimeout [as ontimeout] (timers.js:110:15)
```

It seems like someone forgot an `@` :smile: