(For Carl) Don't use composer for Services_JSON dependency

@cbcase 

`Services_JSON` is a PEAR package and it's causing some issues when we try to load it with Composer. https://github.com/SiftScience/sift-php/issues/10

We already have a copy of `Services_JSON-1.0.3` in the `lib/` directory to support the "manual installation" of the sift client (without composer). We may as well just explicitly `require` that in the two files where we use JSON, instead of trying to make Composer play nicely with PEAR.