Allow customization of the Guzzle client

[baileyherbert]

In environments where a certificate authority bundle is not available or configured, this package will fail with an error:

cURL error 60: SSL certificate problem: unable to get local issuer certificate

Since this issue can't be fixed on the server side in some cases (e.g. shared hosting), I added a $config parameter to the constructor allowing us to pass Guzzle options, including a certificate authority bundle:

$caller = new InsightsCaller($key, 'en', ['verify' => '/path/to/cacert.pem']);

[dsentker]

Great! Thank you,