Added SSL support.

This change simply adds support for a `ssl` config option, to allow for when InfluxDB is being hosted over SSL.

The way it's implemented is that when `ssl` is set to `true`, the `https` module is used for requests to InfluxDB, instead of the `http` module.

Thanks a lot for the library, it's working great.
The `;` needs to be replaced with a `,` here.