Improve JSDoc typings for optional parameters

[daniellockyer]

Hi! Love dockerode 😀

One thing I've noticed is that the JSDoc types for parameters which are optional aren't marked as so, so my editor tends to complain when I use dockerode with no params and Promises. Optional parameters in JSDoc are indicated with square brackets.

For example, container.inspect allows for optional opts and callback: https://github.com/apocas/dockerode/blob/bb88194ff250c4f5b9a0eee2688c5dcc5f623ef9/lib/container.js#L41-L46

In this example, the parameter types should be:

* @param  {Object}   [opts]     Options
* @param  {Function} [callback] Callback

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