Fix parsing of array paths for non standard separators

[boidolr]

Prior to the change arrays only worked with the default separator of ..
So the following currently has different results, even though one would expect them to behave the same:

var Dot = require("dot-object");

// default separator, works as expected:
console.log(Dot.object({'first.name[0]': 'first'}));
// outputs: {first: {name: ["first"]}}

// non standard separator, does not return array:
console.log(new Dot('_').object({'first_name[0]': 'first'}));
// outputs: {first: {name.0: "first"}}

With this fix, the second version gives the same result as the first one.

[boidolr]

@rhalff would it be possible to get this fix included?

[rhalff]

@boidolr Thanks for the PR. This was released as version 2.1.4