Limit on async requests when using more than six data sources

[EricPaulson]

I've been using this library for quite some time, and I've noticed that if I use more than six data sources, only the first six requests are made.

I have eight data sources, but no matter what I do, I'm only seeing requests for the first six. I am using the latest version of this fork.

[AzhurV]

I had the same issue when using typeahead with multiple Bloodhound sources and was able to work around it by including maxPendingRequests in remote for each source, i.e.

var suggestionEngine = new Bloodhound({
    datumTokenizer: Bloodhound.tokenizers.obj.whitespace('value'),
    queryTokenizer: Bloodhound.tokenizers.whitespace,
    remote: {
        url: "myUrl",
        maxPendingRequests: 8,
        ...
    }
});

It seems like the default for maxPendingRequests is 6 based on PR #62. Although even then it seems like requests past the max pending limit should be sent after previous requests have finished rather than just being dropped entirely.