Specifiying a fixedStepSize for ticks should set autoSkip to false

## Expected Behavior

I was expecting `['Options']['scales']['xAxes'][0]['ticks']['fixedStepSize']` = 1;` to give me a step size of 1.

## Current Behavior

I got the step size that chart.js had worked out (2: 40,42,44, etc.).
I had to specify `['Options']['scales']['xAxes'][0]['ticks']['autoSkip'] = false;` to get a step size of 1.

## Possible Solution

Update the docs to mention that this needs to be done. (Easiest)
Or, in the code, set autoSkip to false if you are specifying a step size

## Environment

* Chart.js version: 2.5